The Byzantine navy kept the sea-lanes open for trade and kept supply lines free so the city could not be starved into submission when besieged. In the eighth century, a land and sea attack by Arabs was defeated largely by a secret weapon, Greek fire. This chemical weapon, its composition now unknown, was a sort of liquid napalm that could be sprayed from a hose. The Arab navy was devastated at sea by Greek fire.
In May 1453, Turkish sultan Mehmet II captured a weakly defended Constantinople with the aid of heavy cannon. The fall of the city brought the Byzantine Empire to an end.