d by engines of greater power;
a fleet of Slavonian canoes, which endeavored to force an entrance by
the Golden Horn, was destroyed or driven ashore; the towers with which
they sought to overtop the walls were burnt; and, after ten days of
constantly repeated assaults, the barbarian leader became convinced
that he had undertaken an impossible enterprise, and, having burnt his
engines and his siege works, he retired. The result might have been
different had the Persians, who were experienced in the attack of walled
places, been able to co-operate with him; but the narrow channel which
flowed between Chalcedon and the Golden Horn proved an insurmountable
barrier; the Persians had no ships, and the canoes of the Slavonians
were quite unable to contend with the powerful galleys of the
Byzantines, so that the transport of a body of Persian troops from
Asia to Europe by their aid proved impracticable. Shahr-Barz had the
annoyance of witnessing the efforts and defeat of his allies, without
having it in his power to take any active steps towards assisting the
one or hindering the other.

The war now approached its termination; for the last hope of the
Persians had failed; and Heraclius, with his mind set at rest as
regarded his capital, was free to strike at any part of Persia that he
pleased, and, having the prestige of victory and the assistance of the
Khazars, was likely to carry all before him. It is not clear how he
employed himself during the spring and summer of A.D. 627; but in the
September of that year he started from Lazica with a large Roman army
and a contingent of 40,000 Khazar horse, resolved to surprise
his adversary by a winter campaign, and hoping to take him at a
disadvantage. Passing rapidly through Armenia and Azerbijan without
meeting an enemy that dared to dispute his advance, suffering no
loss except from the guerilla warfare of some bold spirits among
the mountaineers of those regions, he resolved, notwithstanding the
defection of the Khazars, who declined to accompany him further south
than Azerbijan, that he would cross the Zagros mountains into Assyria,
and make a dash at the royal cities of the Mesopotamian region, thus
retaliating upon Chosroes for the Avar attack upon Constantinople of the
preceding year, undertaken at his instigation. Chosroes himself had for
the last twenty-four years fixed his court at Dastagherd in the plain
country, about seventy miles to the north of Ctesiphon. It seemed to