Disclaimer: This is a work of fanfiction based on the Harry Potter series by J. K. Rowling. No disrespect nor any material profit is expected or intended.
Moon and Stone
by Andrea13 and Persephone
The sudden death of one of its Founders was bound to cause a great deal of discussion in the corridors of Hogwarts. Whispers and lowered voices, so as to not disturb the other Founders lost to grief, repeated the tale endlessly.
"It was just all so...sudden! He was always sick a lot, but I still never thought..."
"--seen Professor Hufflepuff? She looks terrible."
"They said it was his heart..."
"I thought he was still young. For a teacher, I mean. He had a few gray hairs, but...well, he was a wizard..."
But stories only stayed simple the first time they were told. With each retelling, more questions were asked and more explanations needed to answer them, and the students added their own memories and speculation to the account their professors had given them.
"I heard Professor Gryffindor and Professor Slytherin were fighting that night."
"Thomas said he was around the corner when it happened and Professor Gryffindor used his sword!"
"Professor Slytherin kept shouting about dangerous beasts he didn't want in the school."
"Professor Gryffindor said they could fight outside or in the Chamber."
The story about the missing fourth Founder became, as most good stories did, something passed on to each year's new students, told at the Welcome Feast after the Sorting Hat did its duty or whispered in the dormitories and classrooms throughout the year.
"He just disappeared after a fight with Professor Gryffindor and they said he died, but he was still really young."
"And he kept raving about monsters in the school."
"He used to not even let Muggle-borns into Slytherin, and that night he was saying he shouldn't have ever let them in."
And over the years, as all those who'd actually known Salazar Slytherin were gone from the school, the stories were still passed on to their children, and to their children's children, and grew ever more fantastic.
"They said he used to disappear all the time, and he used to talk about something called the Chamber."
"What was he doing in it? I heard he had some kind of a monster."
"He hated Muggle-borns! The monster was probably to kill them so he didn't have to put up with them in the school anymore."
"He didn't leave the school; he was forced out after trying to get rid of all the Muggle-borns. He had a big fight with Gryffindor."
Until eventually the truth of Salazar Slytherin was lost to time and only the stories remained.
"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."
...After all, legends always have a basis in fact.
Authors' note: The last version of the story quoted is, of course, the one Professor Binns told the students in class during CoS. "Legends always have a basis in fact" is part of the question Hermione used to talk him into it.