As the Western Roman Empire fell to Germanic tribes and its own internal problems, the Roman Empire in the east, called the Byzantine Empire, flourished.
The Byzantine navy transported soldiers and supplies to help recover the Western Empire. The navy relied on fast galleys called dromons, or racers, to accompany and protect the supply ships. Early dromons had a single bank of oarsmen, but Byzantine shipbuilders later incorporated a second level for oarsmen.
For cargo transport, the Byzantines usually commandeered ordinary merchantmen as transport ships or supply ships. These appear to have been mostly sailing vessels, rather than oared. The Byzantines and Arabs also employed horse-transports, which were either sailing ships or galleys, the latter certainly modified to accommodate the horses.
The origin of the lateen sail has often been attributed by scholars to the Indian Ocean and its introduction into the Mediterranean traditionally ascribed to the Arab expansion of the early-7th century. This was due mainly to the earliest (at that time) iconographic depictions of lateen rigged ships from the Mediterranean post-dating the Islamic expansion into the Mediterranean basin...It was assumed that the Arab people who invaded the Mediterranean basin in the 7th century carried with them the sailing rig familiar to them. Such theories have been superseded by unequivocal depictions of lateen-rigged Mediterranean sailing vessels which pre-date the Arab invasion.