THE GREAT CONQUESTS 29because much of the central forces had probably been spent at Ajnadain
and Damascus. Nevertheless, it was an imposing force, if only in numbers,
and it may have been as strong as 60,000 men.
In spring of 636 the imperial army marched south into Syria. Khalid,
who was by now the de facto commander of the Arab army, promptly
abandoned Damascus, the prize that they had so patiently besieged the
previous year. It is not surprising, since his army would be no better at
defending a city than they had been at attacking one. Their strength was
mobility, and their safety was the desert at their backs. Khalid moved back
to something like the old lines near Deraa, taking up position in about
April 636.
The imperial army approached its old positions, and—not surpris-
ingly—settled into a defensive posture. The Byzantines had a sophisti-
cated, seemingly modern theory of warfare. The army’s goal was to defend
Syria, which they could do from the Deraa position. The destruction of
the Arab army would have been desirable, but the Byzantines saw no
reason to risk a battle if the same outcome—the defense of Syria—could
be obtained without hazard. As a result, the armies faced each other for
weeks on end, stretching through the summer of 636.
Both armies held strong positions for the same reasons—the eastern
flank was covered by the rocky volcanic lava fields of the Jebel Hauran,
and the west flank by the deep canyon and shallow water of the Yarmouk
River. The course of the river itself ran between the two forces. Thus,
both armies may have had relatively secure flanks, and the Muslim forces
had the desert to their rear. It is quite likely that the imperial forces may
have ditched or otherwise fortified their camps, and possibly portions of
the lines.
Much of the detail about the Battle of Yarmouk, as it was styled, is not
known for a certainty, but several theories and threads provide possible
explanations. Over the course of the summer, additional levies were sent
forth by the caliph at Medina, strengthening Khalid’s force. It is likely
that the Byzantines were weakened by desertion at the same time. If this
was so, it may explain why the Byzantines offered battle in August. They
were growing weaker and the enemy stronger, so an early battle was more
to their advantage. If this was the case, it is likely that the imperial forces
attacked, and, once out of their positions, were destroyed by the ferocity
and zeal of the Muslim forces.
Another possible explanation is that the Arabs had infiltrated both flanks
with small parties to block Byzantine communications to the north. When
a great sandstorm blew up from the southern desert—reminiscent of the
storm at the Battle of Qadasiya in 637—the Arabs attacked with the wind