Did they know that it was a tomb, and that knowledge prevailed as some sort of communal memory or was the pyramids' purpose forgotten until recent times and they just knew that it was "there" Curious as to know what Egyptians during this time period thought of the pyramids and other massive structures from Ancient Egypt
Not to discourage any further answers but you'll probably enjoy this older post on Medieval descriptions of the pyramids by /u/khosikulu and /u/sunagainstgold