If it looks human but it shouldn't be there (wherever that is), the answer that immediately seems to spring to mind is: what is a GHOST!*
And since "ghost" stories transcend the usual perceived boundaries of every single time/space continuum – AKA the present – it is somewhat tricky to discuss them here, in this space dedicated to perceived time/space anomalies. Because once the floodgates are open, this space could soon outgrow its carefully trimmed hedges and burst into the anarchy of (yet another!) generically »paranormal« blog. (The fact that the blog mistress is para-normal should be more than enough, for the time being...)
(On the other hand, there are quite a few very good ones that aren't »around«, because the world has simply not heard of them yet.)
I don't know about you, but I've always found it somewhat irritating that so many people – even documentary film-makers and such – jump to conclusions regarding the nature and origins of apparitions and other para-physical phenomena indicating a sort of human presence.
Maybe the local women craved their footwear and the soldiers wouldn't part with it?
And we do know there was a Roman road leading through that future cellar – and that the street level was a feet or two lower than the level of the ground today. Get it? (Or should I say, "Dig it"?)
EDIT (March 18, 2011): The link is dead, and the Wayback Machine does not have it archived. In other words, the article is gone, gone, gone.
Serves me right for being always so ridiculously scrupulous about linking (only) to other sites. I should've snatched the article while it was there!
Anyway, here is a new link: Ciaran Brown Meets Harry Martindale.
(And here is an entry about Roman structures in
However, even the most pedestrian programmes about "haunted" places can yield surprisingly productive thoughts.
So far, so good... But wouldn't you know it: immediately the team proceeded to investigate whether somebody died in that room.
What IF some of the localised, i.e. space-specific, »apparitions« and other, non-visual manifestations of a human »presence« are really the effect of that person's (the ghost-to-be) mental revisiting (remembering, if you will, only with more intensity than usually) the spaces that were important to them – from within their own timeline? Or, perhaps more accurately, across time.
(But more on that some other time. Besides, there is a wonderful collection of books listed on the right side of this page that discuss just that. You don't have to buy them - borrow them, and I am sure at least one or two of them will be worth your while.)