Two major earthquakes (one in 363 AD and the other in 551 AD)
Pet animals like dogs and cats normally get abandoned.
Some people, when they get pets, don't realise the amount of looking after that they need, so they abandon the pets when they become a nuisance.
when babylonia was captured by persia the city of ur which was under the control of persia began to decline. this happend around fourth century bc
Any type of Unexploded bombs that have been abandoned