THE GREAT CONQUESTS 19In fact, all of Khalid’s campaigns show that he truly understood the
concept of “desert power.” Simply put, his men could move into the drier
lands, and his heavier Persian opponents could not. This meant that he
could offer battle or refuse just as he chose. If threatened, his men could
withdraw into the desert where they could not be pursued.
This tactic was certainly obvious to the great warrior. First, his men
were accustomed to the harsh conditions of the desert, and the Persians
were not. Second, the Persian horses would require a great deal of water
daily, and that was not to be found in the sandy wastes. Third, the Arabs
quite naturally employed their camels as mobile supply columns, rather
like convoys of trucks in modern warfare. “Ships of the desert” is an
appropriate phrase.
In late April or early May of 633 the Persians gathered another force
to oppose the raiding Muslims. This probably included a core of Persian
soldiers, but also included a contingent of Arab tribesmen, freshly bribed
by the imperial government. Khalid, hearing of this force, withdrew west
of the Euphrates and gave battle at Ullais. This famous Battle of the Blood
River was apparently a hard fight. The battle name reflects the fact that
Khalid slaughtered all of the enemy prisoners that came under his hand.
Massacres like this were not unheard of in that time, but neither were they
the norm. It is likely that the Muslim leader used the slaughter to send a
clear message to the other tribesmen of the area. This would be a particu-
larly useful message—the Arab desert tribes were the only ones who could
possibly interfere with the “desert power” strategy that the veteran warrior
was employing. Thus, Khalid both defeated a threat to his rear and made
a recurrence less likely.
With the victory at Ullais, and with some reinforcements from the Beni
Temeem, the Muslims moved north, again on the west bank of the Eu-
phrates. They soon confronted and besieged the fortified city of Hira in
May or early June 633.
Hira represented a unique problem to the Arabs, and a common one to
the besieged. As brave as they might be, the lightly equipped desert raiders
would certainly lack the equipment and skills of siege warfare. Defended
walls would present an insurmountable obstacle against which the raiders
could only blockade and harry the surrounding country. This sort of work,
although rewarding, was slow, and brought the attackers to a standstill. If
they remained in place long enough, it was always possible that a fresh
enemy force could arrive from across the Euphrates. It should be noted
that Hira was by far the largest and most formidable city that the Arabs
had yet encountered.