After the fall of the Eastern Roman Empire the struggle on the Mediterranean Sea was held between Byzantine and the Arab world. The dromon became the main type of ships at that time and besides, both opposing sides used them. She was a war ship who dismissed biremes and liburnas. Firstly the dromon was launched about the 6th century A. D. and was used in different variants up to the 12th century. We little know about this ship, however the Byzantine manuscript dated by the year of 850 contains an engraving with the dromon of that period. Her construction resembles that of the bireme with two rows of rowers. She had two masts with Latin sails on them. But the first vessels of such a type had only one row of rowers and they looked like a liburna with a single mast. Later on two- and three-masted dromons appeared. Their length was varied from 30 to 50 m, the width – from 6 to 7 m. There were helms on the stern – one at each side of a board. The ships had sharp forms and were sufficiently fast. The crew consisted of from 100 to 300 people depending on dimensions of a ship. There was another ship in Byzantine called heladion, but we know quite less about her than about the dromon. The dromon’s keel ended by an underwater ram just like for the bireme. The main weapons on the dromon were catapults, which threw fiery shells at a great distance. On the bow and the stern parts of the vessel there were raised decks for bowmen. Powerful and heavy catapults had a possibility to throw shells with the weight of 500 kg at the distance of 1 000 m. Dromons were also armed by light flame-throwers (syphonopho-rami), which flooded enemy ships by fluid burning mass (Greek fire) consisted of tar, sulphur and nitre dissolved in oil. At slight contact with water this fluid blazed up. Such a fire only flamed up in extinguishing by water and it was put out only by wine, vinegar or sand. The precise consistence of such a mixture as well as a construction of weapons did not come to us. Dromons were defended by metal armour against enemy’s rams.