again the Arab force
retired to Cyzicus for the winter.

The Arab commander was determined to stick it out until he had
forced the surrender of the city by sheer exhaustion, but his plan
had a fatal error. During the winter months the land blockade was
abandoned, with the result that supplies for the next year's siege
were readily collected for the beleaguered city. Emperor and citizens
alike rose to the emergency with a spirit of devotion that burned
brighter with every year of the siege. Meanwhile the Christians
of the outlying provinces of Syria and Africa were also fighting
stubbornly and with considerable success against the enemy. The
year 676 passed without any material change in the situation.

[Illustration: CONSTANTINOPLE AND VICINITY]

During the siege a Syrian architect named Callinicus is said to
have come to Constantinople with a preparation of his own invention,
"Greek fire," which he offered the Emperor for use against the Saracen.
This, according to one historian, "was a semi-liquid substance,
composed of sulphur, pitch, dissolved niter, and petroleum boiled
together and mixed with certain less important and more obscure
substances.... When ejected it caught the woodwork which it fell
and set it so thoroughly on fire that there was no possibility
of extinguishing the conflagration. It could only be put out, it
is said, by pouring vinegar, wine, or sand upon it."[1]

[Footnote 1: THE ART OF WAR, Oman, p. 546.]

Constantine IV, the Emperor, was quick to see the possibilities
of the innovation and equipped his dromons with projecting brass
tubes for squirting the substance upon the enemy's ships. These are
sometimes referred to as "siphons," but it is not clear just how
they were operated. One writer[2] is of the opinion that something
of the secret of gunpowder had been obtained from the East and that
the substance was actually projected by a charge of gunpowder;
in short, that these "siphons" were primitive cannon. In addition
to these tubes other means were prepared for throwing the fire.
Earthenware jars containing it were to be flung by hand or arbalist,
and darts and arrows were wrapped with tow soaked in the substance.

[Footnote 2: THE BYZANTINE EMPIRE, Foord, p. 139.]

The Christian fleet was no match for the Saracen in numbers, but
Constantine pinned his faith on the new invention. Accordingly,
during the fourth year of the siege, 677, he boldly led his fleet
to the attack. We have no d