The preservation of the free waterway to the north was all-important to the defence. Accordingly, Leo determined to make a great effort to destroy the Egyptian fleet. His galleys, many of them fitted with apparatus for discharging the famous Greek fire, sailed out suddenly, and fell on the Saracen ships as they lay moored against the Asiatic shore. Many of the crews of the Egyptian ships were Christians, forced on board against their will; these men either deserted to the Imperialists or fled ashore and dispersed. The Moslem sailors on board made some resistance, but being caught at anchor, and unable to manœuvre or escape, they were soon overcome. The whole blockading squadron was burnt or towed back in triumph to Constantinople. The rest of Moslemah’s fleet made no further attempt to bar the Bosphorus, and allowed the Roman galleys to dominate its waters. Leo then threw a force on to the Bithynian shore, and dispersed the Saracen troops who were encamped there. Thus the army of Moslemah was cut off from Asia, and could draw no further supplies from thence. It had already exhausted those of the nearer districts of Thrace, and by the summer of 718 was reduced to the verge of starvation, living from hand to mouth on what its foragers could procure. Many had already perished of privation, when Moslemah heard that a great Bulgarian army had crossed the Balkans, and was advancing against him. Leo had apparently convinced king Terbel that a Saracen invasion of Europe was as dangerous to him as to the empire. Moslemah detached a portion of his army to hold back the Bulgarians, but near Hadrianople it was completely cut to pieces by the barbarians. The Arab historians confess that 22,000 men fell in the rout. This decided Moslemah to raise the siege. His fleet took the remains of the land-army on board, and put it ashore near Cyzicus. [Sidenote: Siege of Constantinople raised, 718.] From thence he forced his way back to Tarsus, but of more than 100,000 men comprised in his original army and its reinforcements, Moslemah brought back only 30,000. The fleet fared yet worse; it was caught in a storm off the Lycian coast, and almost entirely destroyed. The Romans captured many of the surviving ships, and it is said that only five vessels out of a thousand got back to Syria.