How Was the Legend of the Chamber of Secrets Established?

Question

This is the second of a three-part question on the basilisk plot in Harry Potter and the Chamber of Secrets that I'm looking for CANON COMPLIANT explanations for. By "canon compliant", I mean within the spirit of canon, answers directly from the book(s), or quotes from J.K. Rowling.¹

• Professor Binns says, "The whole thing is arrant nonsense, of course," he said. "Naturally, the school has been searched for evidence of such a chamber, many times, by the most learned witches and wizards. It does not exist. A tale told to frighten the gullible." (CoS - page 151 - US Hardcover)
• Professor Binns also says, "Reliable historical sources tell us this much," he said. "But these honest facts have been obscured by the fanciful legend of the Chamber of Secrets. The story goes that Slytherin had built a hidden chamber in the castle, of which the other founders knew nothing. Slytherin, according to the legend, sealed the Chamber of Secrets so that none would be able to open it until his own true heir arrived at the school. The heir alone would be able to unseal the Chamber of Secrets, unleash the horror within, and use it to purge the school of all who were unworthy to study magic." (CoS - pages 150-151 - US Hardcover)

If none of the other three Founders were aware of the existence of Slytherin's Chamber, and Slytherin himself was keeping the existence of the Chamber a secret, how was the legend established?

¹ _{I find the Harry Potter Wiki to be inconsistent and oftentimes incorrect. I am not looking for any answer(s) from the HP Wiki. Just an FYI.}

Question One - How Did Hogwarts Feasibly Accommodate a Basilisk 800-1000+ Years Ago

Question Three - How Did Tom Riddle Find Out About the Existence/Location of the Chamber of Secrets?

Answer 1

Very interesting, indeed. I don't think Salazar Slytherin would have been so pompous as to call his own chamber the chamber of secrets. It would have held no secrets for him. The naming convention alone makes me believe the seed of the legend was not planted by him. If I can declare by the above assumptions that any eligible candidate for the origin of the legend must

1. Have knowledge or reasonable suspicions of the existence of the Chamber.
2. Be unaware of its purpose and/or contents to a degree to be able to say that it is a Chamber of *Secrets*.

That would limit, in my eyes, the origins to descendants of Slytherin, where their knowledge would come from family legends, old stories, etc. Any descendant of Slytherin could have started the legends by simply bragging about their family history. Anyone to whom they bragged could have spread the word. I don't think any direct descendant with even a limited knowledge would have publicly announced that knowledge, but a confidant who was not so faithful could have let the rumor slip.

Unless another wizard researched Slytherin after his death and found evidence about the Chamber. Maybe a diary? or he could have interviewed family members who didn't put much stock into the family stories.

No matter what theory I come up with, there had to be a slip up of his secrecy somewhere. Whether that be to his family, a trusted confidant, or he wrote it down... We can only guess. Each is as likely as the next with the little solid facts we are given on the subject.

Answer 2

The Heirs of Slytherin bragged about it

As Rowling writes on Pottermore:

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.

Slytherin himself bragged about it

From the same source:

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.

Answer 3

[The other founders didn't know about it] + [the chamber was sealed] ≠ [nobody else knew about it]

In other words, the possibility exists that Salazar told his close friends. It seems likely, for example, that the first batch of students in Slytherin knew about it and passed on the knowledge to their children. There's also the people who built the chamber, since Binns implies that Salazar didn't go around with a masonry trowel himself ("...Slytherin had built a hidden chamber...").

Answer 4

In general I agree with the answer from Sheph

It doesn't make sense that Salazar would refer to his own chamber as the chamber of secrets, but he might have referred to it as his secret chamber. Later rumors might have changed that to chamber of secrets.

It doesn't make sense to assume the he didn't tell anybody about the chamber, it would be useless after his death if nobody knew about it. So he would have told his children, and maybe trusted friends, and the children may have told their friends. I wouldn't call this bragging, because for me that word implies that he wants it to be known, and that is inconsistent with wanting to keep it a secret.

The vague details suggest that the secret wasn't directly told by someone who knew. It seems more likely that someone overheard part of a discussion, or that someone hinted at the existence of the chamber, maybe suspecting that the other one would already know about it.

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This part was written while the question was titled "How Was the Legend of the Basilisk Established?"

In canon there is no legend about a Basilisk, just a legend about the Chamber of Secrets that may contain a monster, not specifically a Basilisk.

When Hermione is petrified in the infirmary, Harry and Ron find out that she holds a page from a book in her hand.

Hermione’s hand was clamped so tightly around the paper that Harry was sure he was going to tear it. ... It was a page torn from a very old library book.

It goes on to describe the Basilisk.

Of the many fearsome beasts and monsters that roam our land, there is none more curious or more deadly than the Basilisk, known also as the King of Serpents. This snake, which may reach gigantic size, and live many hundreds of years, is born from a chicken’s egg, hatched beneath a toad. Its methods of killing are most wondrous, for aside from its deadly and venomous fangs, the Basilisk has a murderous stare, and all who are fixed with the beam of its eye shall suffer instant death. Spiders flee before the Basilisk, for it is their mortal enemy, and the Basilisk flees only from the crowing of the rooster, which is fatal to it.

This is just a generic description about Basilisks, probably from some book about dangerous creatures, and not something related to Hogwarts or the Chamber of Secrets.

Hermione added the word "Pipes", so she had figured is out that it is a Basilisk and how it moves around. If there had already been a legend about the Basilisk, she would have known to look up Basilisks and found out much sooner.