Founded in 1348 by Edmund Gonville
, a clergyman who had a hand in quite a lot of pies in mid-fourteenth-century Cambridge
. Its official name was something like "The College of the Blessed Annunciation of the Holy Virgin Mary" but mostly it was called Gonville Hall
It was founded on a spot currently occupied by Corpus Christi College, previously the site of an unfortunate hospital which got knocked down to make room. 5 years after being founded it was being run by Gonville's friend William Bateman, who moved it to its present spot slap bang in the middle of Cambridge with a view to merging it with Trinity Hall, which he'd just founded and which is situated behind Caius. In the end he didn't, which is a Good Thing.
By 1557 it was running out of money. Fortunately, an alumnus named John Keys (Caius) (who was both pretentious and a Renaissance Humanist, making it almost certain that he'd want to spell his name in Latin) was by that time a rich professor in the University of Padua and an expert on classics and medicine. He gave the college a lot of money on the conditions that he be appointed Master
and that it be renamed "Gonville and Caius College". And that's what it is now.
Caius also has possibly the dirtiest front of any Cambridge college, which is unfortunate as it'd be quite pretty if they cleaned it.
Apparently the college features in the film "Chariots of Fire", but I've never seen it so I can't comment.
Re "necessitas": there's a little passageway which has some toilets on it, and it's called the Gate of Necessity. There are some very unclear marks above the arch at one end of it that might say "necessitas", but it's hard to be sure. The regulations book calls it the Gate of Necessity though and that's good enough for me.