gain Greek
fire had proved its deadly efficacy. Elated with this success,
Leo ordered the boom opened wide and, lying in battle order at
the mouth of the Horn, he challenged the Arab fleet to attack. But
such was the terror inspired by Greek fire that the Grand Vizier,
in spite of his enormous superiority in numbers, declined to close.
Instead he withdrew his dromons out of the Bosphorus and thereafter
followed the less risky policy of a blockade. This initial success
of the Christian fleet had the important effect of leaving open
the sea route to the Black Sea, through which supplies could still
reach the beleaguered city.

The Arabs then sat down to wear out the defenders by a protracted
siege on land and sea. In the spring of 718 the new army and the
two new fleets arrived on the scene. One of the latter succeeded,
probably by night, in passing through the Bosphorus and closing
the last inlet to the city. The situation for the defenders became
desperate. Many of the men serving on these new fleets, however,
were Christians. These took every opportunity to desert, and gave
important information to the emperor as to the disposition of the
Arab ships. Acting on this knowledge, Leo took his fleet out from
the shelter of the boom and moved up the straits against the African
and Egyptian squadrons that were blockading the northern exit. The
deserters guided him to where these squadrons lay, at anchor and
unprepared for action. What followed was a massacre rather than
a battle. The Christian members of the crews deserted wholesale
and turned upon their Moslem officers. Ship after ship was rammed
by the Christian dromons or set on fire by the terrible substance
which every Arab regarded with superstitious dread. Some were driven
ashore, others captured, many more sunk or burnt to the water's
edge. Of a total of nearly 800 vessels practically nothing was
left.

Leo followed up this spectacular naval victory by transporting
a force from the garrison of the city to the opposite shore of
the Bosphorus, attacking the army encamped there and driving it
in rout. Meanwhile the Bulgarian chieftain had responded to Leo's
appeal and, relieving the siege of Adrianople, beat back the Saracen
army at that point with great slaughter. The fugitives of that army
served to throw into panic the troops encamped round the walls
of Constantinople, already demoralized by disease, the death of
their leaders, and the annihilation of the African