harry potter - How Was the Legend of the Chamber of Secrets Established?

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

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.