All right, well, I've been on a bit of a historical fix lately - specifically, I have some curiosity regarding the architecture of Hogwarts. Yes, this already sounds boring, but hear me out!
A good place to start before further progressing into this post is E. D. Blanning's "...over a thousand years ago..." Britain at the founding of Hogwarts essay. :]
According the Blanning, we ought to ignore the dozens of anachronisms riddling Rowling's work. But, at least for the sake of the fanfiction I intend to write, I would like to be as historically accurate as possible - but the question is, to which era am I supposed to be loyal? This is more an opinion thing than anything else, so a hand would be appreciated.
I'd like to ask you this: what do you suppose Hogwarts looked like in the day of the Founders? There's more to it than that, though. It really starts with, "When did the Founders actually exist?" It's been suggested that Hogwarts was founded on the close of the tenth century, encroaching on the new millenium, because canon states its foundation "over a thousand years ago" from when Harry begins Hogwarts. But in reality, that leaves quite a bit of leeway!
As for the founding of "Hogwarts", what was the school of witchcraft and wizardry? Some universities did exist at the time, but only for the most wealthy - and secular education didn't really kick off until the Enlightenment in the Renaissance. Was it initially the castle we now know it as? Was it made of stone or timber? And what about the Chamber of Secrets? If I'm not mistaken [which I very well may be], sewage systems originated in Rome - but much of Roman technology was wiped out by the Germanic invasions in the centuries before Hogwarts' foundation.
As for the stone/timber question, there were very few stone castles until the 1200s a.d. of any note. Admittedly, the Welsh were a bit ahead of the times in this area - but the Welsh weren't exactly occupying Scotland, where Hogwarts should have been located. The area, I suspect, would have been more dominated by Norman architecture of wood.
So, what do you think is more appropriate, as far as the time setting of the Founders and Hogwarts? Right now, for my story, I'm leaning towards a small wooden keep with the traditional motte-and-bailey set-up, though I suspect there will have to be some renewal of Roman influence later down the line. Still in some debate. As a reader, though, what would you find most believable?