A metal object (alum still counts as metal, right?) floats feather lightly upon the waters of a ditch into a sealed stone building?
Oh those archeologists. They say the darnedest things.
Occam’s razor says it was put there by a time traveling angel of the Lord which happened to have a taste for Tuborg beer.
Water also moves boulders. But hey, no one could fault a time traveling angel of the Lord for stopping for a wee nip.