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In choosing the number of the concealed platform that would take young witches and wizards to boarding school, I decided that it would have to be a number between those of the Muggle platforms – therefore, it was clearly a fraction. This raised the interesting question of how many other fractional platforms lay between the whole-numbered platforms at King’s Cross, and I concluded that there were probably quite a few. Although these are never mentioned in the book, I like to think that it is possible to take a version of the Orient Express off to wizard-only villages in continental Europe (try platform seven and a half), and that other platforms may be opened on an as-required-basis, for instance for large, one-off events such as Celestina Warbeck concerts (see your ticket for details).

The number nine and three-quarters presented itself without much conscious thought, and I liked it so much that I took it at once. It is the ‘three-quarters’ that makes it, of course.

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First-year Hogwarts students are hustled into the Great Hall for the wizarding world’s most discerning personality test. As each young witch and wizard is called forward, an infinitely wise talking hat is placed on his or her head. We know what the Sorting Hat does, but how much do we know about how it was created?

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An archaic Hogwarts term for any new student whose Sorting takes longer than five minutes. This is an exceptionally long time for the Sorting Hat to deliberate, and occurs rarely, perhaps once every fifty years.

Of Harry Potter’s contemporaries, Hermione Granger and Neville Longbottom came closest to being Hatstalls. The Sorting Hat spent nearly four minutes trying to decide whether it should place Hermione in Ravenclaw or Gryffindor. In Neville’s case, the Hat was determined to place him in Gryffindor: Neville, intimidated by that house’s reputation for bravery, requested a placing in Hufflepuff. Their silent wrangling resulted in triumph for the Hat.

The only true Hatstalls known personally to Harry Potter were Minerva McGonagall and Peter Pettigrew. The former caused the Hat to agonise for five and a half minutes as to whether Minerva ought to go to Ravenclaw or Gryffindor; the latter was placed in Gryffindor after a long deliberation between that house and Slytherin. The Sorting Hat, which is infamously stubborn, still refuses to accept that its decision in the case of the latter may have been erroneous, citing the manner in which Pettigrew died as (dubious) evidence.

The Hufflepuff common room is entered from the same corridor as the Hogwarts kitchens. Proceeding past the large still life that forms the entrance to the latter, a pile of large barrels is to be found stacked in a shadowy stone recess on the right-hand side of the corridor. The barrel two from the bottom, middle of the second row, will open if tapped in the rhythm of ‘Helga Hufflepuff’.[1] As a security device to repel non-Hufflepuffs, tapping on the wrong barrel, or tapping the incorrect number of times, results in one of the other lids bursting off and drenching the interloper in vinegar.

A sloping, earthy passage inside the barrel travels upwards a little way until a cosy, round, low-ceilinged room is revealed, reminiscent of a badger’s set. The room is decorated in the cheerful, bee-like colours of yellow and black, emphasised by the use of highly polished, honey-coloured wood for the tables and the round doors that lead to the boys’ and girls’ dormitories (furnished with comfortable wooden bedsteads, all covered in patchwork quilts).

A colourful profusion of plants and flowers seem to relish the atmosphere of the Hufflepuff common room: various cacti stand on wooden circular shelves (curved to fit the walls), many of them waving and dancing at passers-by, while copper-bottomed plant holders dangling amid the ceiling cause tendrils of ferns and ivies to brush your hair as you pass under them.

A portrait over the wooden mantelpiece (carved all over with decorative dancing badgers) shows Helga Hufflepuff, one of the four founders of Hogwarts School, toasting her students with a tiny, two-handled golden cup. Small, round windows just level with the ground at the foot of the castle show a pleasant view of rippling grass and dandelions, and, occasionally, passing feet. These low windows notwithstanding, the room feels perennially sunny.

Nevertheless, it ought not to be concluded from the above that Hufflepuffs are dimwits or duffers, though they have been cruelly caricatured that way on occasion. Several outstanding brains have emerged from Hufflepuff House over the centuries; these fine minds simply happened to be allied to outstanding qualities of patience, a strong work ethic and constancy, all traditional hallmarks of Hufflepuff House.

When I first planned the series, I expected Harry to visit all four house common rooms during his time at Hogwarts. There came a point when I realised that there was never going to be a valid reason to enter the Hufflepuff room. Nevertheless, it is quite as real to me as the other three, and I always knew exactly where those Hufflepuffs were going when they headed off towards the kitchens after lessons.

Perhaps no students (even including Harry Potter, Ron Weasley, Hermione Granger and Tom Riddle) have ever explored the castle and grounds of Hogwarts as thoroughly and illicitly as the four creators and contributors to the Marauder’s Map: James Potter, Sirius Black, Remus Lupin and Peter Pettigrew.

James, Sirius and Peter were not initially impelled to explore the school grounds by night out of devilment alone (though that played its part), but by their desire to help their dear friend Remus Lupin to bear his lycanthropy. Prior to the invention of the Wolfsbane Potion, Lupin was compelled to undergo an excruciating transformation every full moon. Once his condition was discovered by his three best friends, they sought a way to render his transformations less solitary and painful, which led to them learning to become (unregistered) Animagi, so that they could keep him company without harm to themselves. The ability of Sirius Black, Peter Pettigrew and James Potter to become, respectively, a dog, a rat and a stag, enabled them to explore the castle grounds by night undetected. The interior of the castle, meanwhile, was mapped over time with the help of James Potter’s Invisibility Cloak.

The Marauder’s Map is lasting testimony to the advanced magical ability of the four friends who included Harry Potter’s father, godfather and favourite teacher. The map they created during their time at Hogwarts appears to be a blank piece of parchment unless activated by the phrase: ‘I solemnly swear that I am up to no good’, a phrase that, in the case of three of the four makers, should be understood as a joke. The ‘no good’ of which they wrote never denoted Dark magic, but school rule-breaking; similar bravado is evinced by their use of their own nicknames on the map (‘Messrs Moony, Wormtail, Padfoot and Prongs’).

The magic used in the map’s creation is advanced and impressive; it includes the Homonculous Charm, enabling the possessor of the map to track the movements of every person in the castle, and it was also enchanted to forever repel (as insultingly as possible) the curiosity of their nemesis, Severus Snape.

Although the precise circumstances surrounding the makers’ loss of their map are not given in the Harry Potter novels, it is easy to conclude that they eventually over-reached themselves and were cornered by Argus Filch, probably on a tip-off from Snape, whose obsession it had become to expose his arch-rival, James Potter, in wrong-doing. The masterpiece of a map was confiscated in Sirius, James, Remus and Peter’s final year, and none of them were able to steal it back from a well-prepared and suspicious Filch. In any case, their priorities changed in their final months at school, becoming far more serious and focused on the world beyond Hogwarts, where Lord Voldemort was successfully rising to power. All four of the map’s creators would shortly be inducted into the renegade organisation headed by Albus Dumbledore, the Order of the Phoenix, and a map of their old school – no matter how ingenious – would no longer be of use to them except as a piece of nostalgia.

The Marauder’s Map was, however, of immense use to the young Weasley twins. The story of Fred and George’s acquisition of the map is told in Harry Potter and the Prisoner of Azkaban. It was a mark of their high esteem for Harry Potter, and their belief that he stood in need of assistance with a destiny none of them yet fully understood, that they later gifted the map to him, unwittingly passing it on to the child of one of the creators.

The map was subsequently confiscated from Harry Potter by a Death Eater in disguise at the school, who recognised it as a likely source of his own discovery.

The Marauder’s Map subsequently became something of a bane to its true originator (me), because it allowed Harry a little too much freedom of information. I never showed Harry taking the map back from the empty office of (the supposed) Mad-Eye Moody, and I sometimes regretted that I had not capitalised on this mistake to leave it there. However, I like the moment when Harry watches Ginny’s dot moving around the school in Deathly Hallows, so on balance I am glad I let Harry reclaim his rightful property.

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The grounds of Hogwarts function partly as a nature reserve for magical creatures which have difficulty existing in Muggle-inhabited areas.

The lake is full of creatures that would make a Muggle naturalist swoon with delight – if terror did not seize them first. There are Grindylows (vicious little water demons), merpeople (of a hardy Scottish strain) and a giant squid, which is semi-domesticated and permits students to tickle its tentacles on sunny days, when it basks in the shallows.

Giant squid genuinely exist, though they are most mysterious creatures. Although their extraordinary bodies have been washed up all over the world, it was not until 2006 that a live giant squid was captured on film by Muggles. I strongly suspect them of having magical powers.

The lake is the setting for the second task that the Triwizard competitors must face in Goblet of Fire, which is also my favourite task. I find it satisfyingly creepy; I like the diversity of the methods employed by the competitors to breathe underwater, and I enjoyed plumbing the depths of a part of the grounds that had never been seen before. In the original draft of Chamber of Secrets, I had Harry and Ron crash into the lake in Mr Weasley’s Ford Anglia, and meet the merpeople there for the first time.

At that time I had a vague notion that the lake might lead to other places, and that the merpeople might play a larger role in the later books than they did, so I thought that Harry ought to be introduced to both at this stage. However, the Whomping Willow provided a more satisfying, less distracting crash, and served a later purpose in Prisoner of Azkaban, too. The Great Lake (which is really a Scottish loch, apparently freshwater and landlocked) never did develop as a portal to other seas or rivers, although the appearance of the Durmstrang ship from its depths in Goblet of Fire hints at the fact that if you are travelling by an enchanted craft, you might be able to take a magical shortcut to other waterways.‌

All first-years at Hogwarts must take seven subjects: Transfiguration, Charms, Potions, History of Magic, Defence Against the Dark Arts, Astronomy and Herbology. Flying lessons (on broomsticks) are also compulsory.

At the end of their second year at Hogwarts, students are required to choose a minimum of two more subjects from the following list: Arithmancy, Muggle Studies, Divination, Study of Ancient Runes and Care of Magical Creatures.

Very specialised subjects such as Alchemy are sometimes offered in the final two years, if there is sufficient demand.

A slightly different list of school subjects appears in my earliest notes. Herbology is called ‘Herbalism’, Divination is compulsory from the first year, as are Alchemy and a subject called simply ‘Beasts’, whereas Transfiguration is called ‘Transfiguration/Metamorphosis’.

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In spite of the many Muggle fantasies around the subject, time travel is possible in only a limited sense even in the magical world. While the subject is shrouded in great secrecy – investigations are ongoing in the Department of Mysteries – it appears that magic can take you only so far.

According to Professor Saul Croaker, who has spent his entire career in the Department of Mysteries studying time-magic:

‘As our investigations currently stand, the longest period that may be relived without the possibility of serious harm to the traveller or to time itself is around five hours. We have been able to encase single Hour-Reversal Charms, which are unstable and benefit from containment, in small, enchanted hour-glasses that may be worn around a witch or wizard’s neck and revolved according to the number of hours the user wishes to relive.

‘All attempts to travel back further than a few hours have resulted in catastrophic harm to the witch or wizard involved. It was not realised for many years why time travellers over great distances never survived their journeys. All such experiments have been abandoned since 1899, when Eloise Mintumble became trapped, for a period of five days, in the year 1402. Now we understand that her body had aged five centuries in its return to the present and, irreparably damaged, she died in St Mungo’s Hospital for Magical Maladies and Injuries shortly after we managed to retrieve her. What is more, her five days in the distant past caused great disturbance to the life paths of all those she met, changing the course of their lives so dramatically that no fewer than twenty-five of their descendants vanished in the present, having been “un-born”.

‘Finally, there were alarming signs, during the days following Madam Mintumble’s recovery, that time itself had been disturbed by such a serious breach of its laws. Tuesday following her reappearance lasted two and a half full days, whereas Thursday shot by in the space of four hours. The Ministry of Magic had a great deal of trouble in covering this up and since that time, the most stringent laws and penalties have been placed around those studying time travel.’

Even the use of the very limited amount of Time-Turners at the Ministry’s disposal is hedged around with hundreds of laws. While not as potentially dangerous as skipping five centuries, the re-use of a single hour can still have dramatic consequences and the Ministry of Magic seeks the strictest guarantees if it permits the use of these rare and powerful objects. It would surprise most of the magical community to know that Time-Turners are generally only used to solve the most trivial problems of time-management and never for greater or more important purposes, because, as Saul Croaker tells us, ‘just as the human mind cannot comprehend time, so it cannot comprehend the damage that will ensue if we presume to tamper with its laws.’

The Ministry’s entire stock of Time-Turners was destroyed during a fight in the Department of Mysteries about three years after Hermione Granger was granted permission to use one at Hogwarts.

I went far too light-heartedly into the subject of time travel in Harry Potter and the Prisoner of Azkaban. While I do not regret it (Prisoner of Azkaban is one of my favourite books in the series), it opened up a vast number of problems for me, because after all, if wizards could go back and undo problems, where were my future plots?

I solved the problem to my own satisfaction in stages. Firstly, I had Dumbledore and Hermione emphasise how dangerous it would be to be seen in the past, to remind the reader that there might be unforeseen and dangerous consequences as well as solutions in time travel. Secondly, I had Hermione give back the only Time-Turner ever to enter Hogwarts. Thirdly, I smashed all remaining Time-Turners during the battle in the Department of Mysteries, removing the possibility of reliving even short periods in the future.

This is just one example of the ways in which, when writing fantasy novels, one must be careful what one invents. For every benefit, there is usually a drawback.‌

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In spite of the unfounded rumours surrounding the Shrieking Shack, which was never haunted at all, Hogwarts is the most heavily haunted dwelling place in Britain (and this is against stiff competition, as there are more reported ghost sightings/sensings on these damp islands than anywhere else in the world). The castle is a congenial place for ghosts, because the living inhabitants treat their dead friends with tolerance and even affection, no matter how many times they have heard the same old reminiscences.

Each of the four Hogwarts houses has its own ghost. Slytherin boasts the Bloody Baron, who is covered in silver bloodstains. The least talkative of the house ghosts is the Grey Lady, who is long-haired and beautiful.

Hufflepuff House is haunted by the Fat Friar, who was executed because senior churchmen grew suspicious of his ability to cure the pox merely by poking peasants with a stick, and his ill-advised habit of pulling rabbits out of the communion cup. Though a genial character in general, the Fat Friar still resents the fact that he was never made a cardinal.

Gryffindor house is home to Nearly Headless Nick, who in life was Sir Nicholas de Mimsy-Porpington. Something of a snob, and a less accomplished wizard than he believed, Sir Nicholas lounged around the court of Henry VII in life, until his foolish attempt to beautify a lady-in-waiting by magic caused the unfortunate woman to sprout tusks. Sir Nicholas was stripped of his wand and inexpertly executed, leaving his head hanging off by a single flap of skin and sinew. He retains a feeling of inadequacy with regard to truly headless ghosts.

Another notable Hogwarts ghost is Moaning Myrtle, who haunts an unpopular girls’ toilet. Myrtle was a student at Hogwarts when she died, and she chose to return to school in perpetuity, with the short-term aim of haunting her arch-rival and bully, Olive Hornby. As the decades have rolled by, Myrtle has made a name for herself as the most miserable ghost in school, usually to be found lurking inside one of the toilets and filling the tiled space with her moans and howls.

The inspiration for Moaning Myrtle was the frequent presence of a crying girl in communal bathrooms, especially at the parties and discos of my youth. This does not seem to happen in male bathrooms, so I enjoyed placing Harry and Ron in such uncomfortable and unfamiliar territory in Harry Potter and the Chamber of Secrets and Harry Potter and the Half-Blood Prince.

The most productive ghost at Hogwarts is, of course, Professor Binns, the old History of Magic teacher who fell asleep in front of the staff-room fire one day and simply got up to give his next class, leaving his body behind. There is some debate as to whether or not Professor Binns realises he is dead. While his entrance to lessons through the blackboard is vaguely amusing the first time students see it, he is not the most stimulating teacher.

The inspiration for Professor Binns was an old professor at my university, who gave every lecture with his eyes closed, rocking backwards and forwards slightly on his toes. While he was a brilliant man, who disgorged an immense amount of valuable information at every lecture, his disconnect with his students was total. Professor Binns is only dimly aware of his living students, and is astonished when they begin asking him questions.

In the very earliest list of ghosts I ever wrote for Hogwarts, I included Myrtle (initially named ‘Wailing Wanda’), Professor Binns, the Grey Lady (then called ‘the Whispering Lady’) and the Bloody Baron. There was also a Black Knight, The Toad (which left ectoplasm all over its classroom), and a ghost I rather regret not using: his name was Edmund Grubb, and the notes beside his name say: Expired in the doorway of the Dining Hall. Sometimes stops people getting in, out of spite. Fat Victorian ghost. (Ate poisonous berries).

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In the world of Harry Potter, a ghost is the transparent, three-dimensional imprint of a deceased witch or wizard, which continues to exist in the mortal world. Muggles cannot come back as ghosts, and the wisest witches and wizards choose not to. It is those with ‘unfinished business’, whether in the form of fear, guilt, regrets or overt attachment to the material world, who refuse to move on to the next dimension.

Having chosen a feeble simulacrum of mortal life, ghosts are limited in what they can experience. No physical pleasure remains to them, and their knowledge and outlook remains at the level it had attained during life, so that old resentments (for instance, at having an incompletely severed neck) continue to rankle after several centuries. For this reason, ghosts tend to be poor company, on the whole. They are especially disappointing on the one subject that fascinates most people: ghosts cannot return a very sensible answer on what it is like to die, because they have chosen an impoverished version of life instead.

Ghosts can pass through solid objects without causing damage to themselves or the material, but create disturbances in water, fire and air. The temperature drops in the immediate vicinity of a ghost, an effect intensified if many congregate in the same place. Their appearance can also turn flames blue. Should part or all of a ghost pass through a living creature, the latter will experience a freezing sensation as though they have been plunged into ice-cold water.

Witches and wizards are much more susceptible to what Muggles call paranormal activity, and will see (and hear) ghosts plainly, where a Muggle might only feel that a haunted place is cold or ‘creepy’. Muggles who insist that they see ghosts in perfect focus are either a) lying or b) wizards showing off – and in flagrant breach of the International Statute of Secrecy.

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Hogwarts portraits are able to talk and move around from picture to picture. They behave like their subjects. However, the degree to which they can interact with the people looking at them depends not on the skill of the painter, but on the power of the witch or wizard painted.

When a magical portrait is taken, the witch or wizard artist will naturally use enchantments to ensure that the painting will be able to move in the usual way. The portrait will be able to use some of the subject’s favourite phrases and imitate their general demeanour. Thus, Sir Cadogan’s portrait is forever challenging people to a fight, falling off its horse and behaving in a fairly unbalanced way, which is how the subject appeared to the poor wizard who had to paint him, while the portrait of the Fat Lady continues to indulge her love of good food, drink and tip-top security long after her living model passed away.

However, neither of these portraits would be capable of having a particularly in-depth discussion about more complex aspects of their lives: they are literally and metaphorically two-dimensional. They are only representations of the living subjects as seen by the artist.

Some magical portraits are capable of considerably more interaction with the living world. Traditionally, a headmaster or headmistress is painted before their death. Once the portrait is completed, the headmaster or headmistress in question keeps it under lock and key, regularly visiting it in its cupboard (if so desired) to teach it to act and behave exactly like themselves, and imparting all kinds of useful memories and pieces of knowledge that may then be shared through the centuries with their successors in office.

The depth of knowledge and insight contained in some of the headmasters’ and headmistresses’ portraits is unknown to any but the incumbents of the office and the few students who have realised, over the centuries, that the portraits’ apparent sleepiness when visitors arrive in the office is not necessarily genuine.

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The Mirror of Erised is a very old device. Nobody knows who created it, or how it came to be at Hogwarts School. A succession of teachers have brought back interesting artefacts from their travels, so it might have arrived at the castle in this casual manner, either because the teacher knew how it worked and was intrigued by it, or because they did not understand it and wished to ask their colleagues’ opinions.

The Mirror of Erised is one of those magical artefacts that seems to have been created in a spirit of fun (whether innocent or malevolent is a matter of opinion), because while it is much more revealing than a normal mirror, it is interesting rather than useful. Only after Professor Dumbledore makes key modifications to the mirror (which has been languishing in the Room of Requirement for a century or so before he brings it out and puts it to work) does it become a superb hiding place, and the final test for the impure of heart.

The mirror’s inscription (‘erised stra ehru oyt ube cafru oyt on wohsi’) must be read backwards to show its true purpose.

Albus Dumbledore, who brings it out of hiding, puts it back where he found it when it has achieved his purpose in Philosopher’s Stone. We must conclude, therefore, that the mirror was destroyed, along with all the other contents of the Room of Requirement, during the Battle of Hogwarts.

Albus Dumbledore’s words of caution to Harry when discussing the Mirror of Erised express my own views. The advice to ‘hold on to your dreams’ is all well and good, but there comes a point when holding on to your dreams becomes unhelpful and even unhealthy. Dumbledore knows that life can pass you by while you are clinging on to a wish that can never be – or ought never to be – fulfilled. Harry’s deepest yearning is for something impossible: the return of his parents. Desperately sad though it is that he has been deprived of his family, Dumbledore knows that to sit gazing on a vision of what he can never have, will only damage Harry. The mirror is bewitching and tantalising, but it does not necessarily bring happiness.

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A Pensieve is a wide and shallow dish made of metal or stone, often elaborately decorated or inlaid with precious stones, and carrying powerful and complex enchantments. Pensieves are rare, because only the most advanced wizards ever use them, and because the majority of wizardkind is afraid of doing so.

The perceived dangers of the Pensieve relate to its power over memory or thought. The Pensieve is enchanted to recreate memories so that they become re-liveable, taking every detail stored in the subconscious and recreating it faithfully, so that either the owner, or (and herein lies the danger) a second party, is able to enter the memories and move around within them. Inevitably, those with things to hide, those ashamed of their pasts, those eager to keep hold of their secrets, or protective of their privacy, will be wary of an object like the Pensieve.

Even more difficult than the recreation of memories is the use of a Pensieve to examine and sort thoughts and ideas, and very few wizards have the ability to do so. Albus Dumbledore is seen using the Hogwarts Pensieve in this way, notably in Chapter Thirty of Harry Potter and the Goblet of Fire, when he adds thoughts to the Pensieve and Harry’s face turns into Snape’s; Dumbledore is reminding himself of the hidden connection between Snape and Harry (that Snape was in love with Harry’s mother, and is now – though immensely grudgingly – honour-bound to protect him).

Traditionally, a witch or wizard’s Pensieve, like their wand, is buried with them, as it is considered an intensely personal artefact; any thoughts or memories left inside the Pensieve are likewise interred with their owner, unless he or she has requested otherwise. The Hogwarts Pensieve, however, belongs not to any individual but to the school. It has been used by a long line of headmasters and headmistresses, who have also left behind their life experience in the form of memories. This forms an invaluable library of reference for the headmaster or headmistress of the day.

The Hogwarts Pensieve is made of ornately carved stone and is engraved with modified Saxon runes, which mark it as an artefact of immense antiquity that pre-dates the creation of the school. One (unsubstantiated) legend says that the founders discovered the Pensieve half-buried in the ground on the very spot where they decided to erect their school.

The name ‘Pensieve’ is a homonym of ‘pensive’, meaning deeply, seriously thoughtful; but it also a pun, the ‘sieve’ part of the word alluding to the object’s function of sorting meanings from a mass of thoughts or memories.

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I did not invent the concept of the Philosopher’s Stone, which is a legendary substance that was once believed to be real, and the true goal of alchemy.

The properties of ‘my’ Philosopher’s Stone conform to most of the attributes the ancients ascribed to it. The Stone was believed to turn base metals into gold, and also to produce the Elixir of Life, which could make you immortal. ‘Genuine’ alchemists – the forerunners of chemists and physicists – such as Sir Isaac Newton and (the real) Nicolas Flamel, sought, sometimes over lifetimes, to discover the secret of its creation.

The Stone is variously described as red and white in the many old texts in which it appears. These colours are important in most accounts of alchemy, and are often interpreted as having symbolic meaning.

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The sword of Gryffindor was made a thousand years ago by goblins, the magical world’s most skilled metalworkers, and is therefore enchanted. Fashioned from pure silver, it is inset with rubies, the stone that represents Gryffindor in the hour-glasses that count the house points at Hogwarts. Godric Gryffindor’s name is engraved just beneath the hilt.

The sword was made to Godric Gryffindor’s specifications by Ragnuk the First, finest of the goblin silversmiths, and therefore King (in goblin culture, the ruler does not work less than the others, but more skillfully). When it was finished, Ragnuk coveted it so much that he pretended that Gryffindor had stolen it from him, and sent minions to steal it back. Gryffindor defended himself with his wand, but did not kill his attackers. Instead he sent them back to their king bewitched, to deliver the threat that if he ever tried to steal from Gryffindor again, Gryffindor would unsheathe the sword against them all.

The goblin king took the threat seriously and left Gryffindor in possession of his rightful property, but remained resentful until he died. This was the foundation for the false legend of Gryffindor’s theft that persists, in some sections of the goblin community, to this day.

The question of why a wizard would need a sword, though often asked, is easily answered. In the days before the International Statute of Secrecy, when wizards mingled freely with Muggles, they would use swords to defend themselves just as often as wands. Indeed, it was considered unsporting to use a wand against a Muggle sword (which is not to say it was never done). Many gifted wizards were also accomplished duellists in the conventional sense, Gryffindor among them.

Much like a magic wand, the sword of Gryffindor appears to be almost sentient, responding to appeals for help by Gryffindor’s chosen successors; and, similar to a wand, part of its magic is that it imbibes that which strengthens it, which can then be used against enemies.

There have been many enchanted swords in folklore. The Sword of Nuadu, part of the four legendary treasures of Tuatha Dé Danann, was invincible when drawn. Gryffindor’s sword owes something to the legend of Excalibur, the sword of King Arthur, which in some legends must be drawn from a stone by the rightful king. The idea of fitness to carry the sword is echoed in the sword of Gryffindor’s return to worthy members of its true owner’s house.

There is a further allusion to Excalibur emerging from the lake when Harry must dive into a frozen forest pool to retrieve the sword in Deathly Hallows (though the location of the sword was really due to a spiteful impulse of Snape’s to place it there), for in other versions of the legend, Excalibur was given to Arthur by the Lady of the Lake, and was returned to the lake when he died.

Within the magical world, physical possession is not necessarily a guarantee of ownership. This concept applies to the three Deathly Hallows, and also to Gryffindor’s sword.

I am interested in what happens when cultural beliefs collide. In the Harry Potter books, the most militant of the goblin race consider all goblin-made objects to be theirs by right, although a specific object might be made over to a wizard for his lifespan upon a payment of gold. Witches and wizards, like Muggles, believe that once payment has been made, the object belongs to them and their descendants or legatees in perpetuity. This is a clash of values without a solution, because each side has a different concept of what is right. It therefore presents Harry with a difficult moral dilemma when Griphook demands the sword as payment for his services in Deathly Hallows.

The subterranean Chamber of Secrets was created by Salazar Slytherin without the knowledge of his three fellow founders of Hogwarts. The Chamber was, for many centuries, believed to be a myth; however, the fact that rumours of its existence persisted for so long reveals that Slytherin spoke of its creation and that others believed him, or else had been permitted, by him, to enter.

There is no doubt that each of the four founders sought to stamp their own mark upon the school of witchcraft and wizardry that they intended would be the finest in the world. It was agreed that each would construct their own houses, for example, choosing the location of common rooms and dormitories. However, only Slytherin went further, and built what was in effect a personal, secret headquarters within the school, accessible only by himself or by those he allowed to enter.

Perhaps, when he first constructed the Chamber, Slytherin wanted no more than a place in which to instruct his students in spells of which the other three founders may have disapproved (disagreements sprung up early around the teaching of the Dark Arts). However, it is clear by the very decoration of the Chamber that by the time Slytherin finished it he had developed grandiose ideas of his own importance to the school. No other founder left behind them a gigantic statue of themselves or draped the school in emblems of their own personal powers (the snakes carved around the Chamber of Secrets being a reference to Slytherin’s powers as a Parselmouth).

What is certain is that by the time Slytherin was forced out of the school by the other three founders, he had decided that henceforth, the Chamber he had built would be the lair of a monster that he alone – or his descendants – would be able to control: a Basilisk. Moreover, only a Parselmouth would be able to enter the Chamber. This, he knew, would keep out all three founders and every other member of staff.

The existence of the Chamber was known to Slytherin’s descendants and those with whom they chose to share the information. Thus the rumour stayed alive through the centuries.

There is clear evidence that the Chamber was opened more than once between the death of Slytherin and the entrance of Tom Riddle in the twentieth century. When first created, the Chamber was accessed through a concealed trapdoor and a series of magical tunnels. However, when Hogwarts’ plumbing became more elaborate in the eighteenth century (this was a rare instance of wizards copying Muggles, because hitherto they simply relieved themselves wherever they stood, and vanished the evidence), the entrance to the Chamber was threatened, being located on the site of a proposed bathroom. The presence in school at the time of a student called Corvinus Gaunt – direct descendant of Slytherin, and antecedent of Tom Riddle – explains how the simple trapdoor was secretly protected, so that those who knew how could still access the entrance to the Chamber even after newfangled plumbing had been placed on top of it.

Whispers that a monster lived in the depths of the castle were also prevalent for centuries. Again, this is because those who could hear and speak to it were not always as discreet as they might have been: the Gaunt family could not resist boasting of their knowledge. As nobody else could hear the creature sliding beneath floorboards or, latterly, through the plumbing, they did not have many believers, and none, until Riddle, dared unleash the monster on the castle.

Successive headmasters and mistresses, not to mention a number of historians, searched the castle thoroughly many times over the centuries, each time concluding that the Chamber was a myth. The reason for their failure was simple: none of them was a Parselmouth.