Excavations in the ancient port at Unguja Ukuu on the island of Zanzibar suggest that the Romans' appetite for ivory indirectly caused the end of their empire, and the start of the dark ages. In the 6th century AD ivory from the abundant herds of African elephants was shipped to Justinian's court at Constantinople from Zanzibar - but on the outward voyage there were the usual stowaways: rats. These would have been black rats (rattus rattus) - whose bones have been found together with typical contemporary Mediterranean pottery. The black rat is not indigenous to Africa, and must have arrived on board ship - then fraternised with the local rodents (immune to the plague which their fleas carried). Then they got back on board, taking the plague back in the ships' holds along with the ivory. The plague arrived in Constantinople in 541 AD - and started killing up to 16,000 people a day. Byzantine officials stopped counting the bodies when the toll passed a quarter of a million. Within ten years it had swept across Europe, and the Dark Ages had begun. [The Times - article and pictures June 8th 1999]