ADMINISTRATIONtheir oases. The conquest had the immediate effect of shifting the
important defensive frontier of Iraq from the southwest against the
Arabs in the desert to the northeast against the Persians on the plateau,
and this tended to remain the case even after the conquest of Iran.
'Ayn Tamr belonged to the frontier district of Hira in the late
Sasanian period and was the largest and most important of the oases
at the northwest end of the line of Persian defenses.177 At the time of
the conquest, the Persian garrison at 'Ayn Tamr was commanded by
Mihriin, the son of Bahram Chiibin,178 and, after defeating him, Khalid
left 'Uwaym ibn al-Kahl al-Aslami as his lieutenant there.179 'Ayn
T amr preserved its military character as a frontier post in the early
Islamic period because of its location on the side of Iraq facing Syria.
During the first and second (itnas, 'Ayn Tamr was garrisoned as an
important defensive point against Syrian attack.1^80
Kufa more than replaced Hira as a local administrative center be-
cause the territory administered by the Muslim governors of Kufa
combined several former Sasanian provinces. The territory immedi-
ately under the authority of the Muslim governors at Kufa combined
the region irrigated by the Euphrates with the frontier district of Hira.
There were usually subordinate military governors with garrisons at
Anbar and 'Ayn Tamr. Beginning in the caliphate of 'Umar I, the
region irrigated by the Euphrates served as a single jurisdiction for
tax collectors.
Beyond the Tigris, the territory of Ard Jukha was administered by
officers appointed by the governor of Kufa, with their post and garrison
at Mada'in. Hulwan and Mah of Kufa were under other subordinate
officers, and, in 638, when the Muslim army settled at Kufa, its frontier
posts were at Hulwan, Masabadhan, Qarqisiyya, and Mawsil.1^81 After
the conquest of the Jazira was completed, the territory of Kufa only
went as far as 'Anat on the middle Euphrates, and from the time of
'Uthman the appointment of a governor for Mawsil tended to be
made by the caliph. Consequently, the Sawad of Kufa came to be
defined as the region extending from Kaskar to the Zab and from
Hulwan to Qadisiyya.^182 An indication of how the subordinate divi-
177 Ibn Khurradadhbih, (Masalik, p. 8) and Yaqiit (Buldan, I, 770) put 'Ayn Tamr
in the kura of Upper Bihqubadh.
178 BaiadhurI, Futu~, p. 246; Tabari, Ta'rikh, I, 2062-63.
179 For events at 'Ayn Tamr, see ai-'Aii, "Min!aqat ai-Kiifa," pp. 242-44.
180 Tabari, Ta'rikh, I, 2065.
181 Ibid., I, 2497.
182 Ibn Qutayba, al-Ma'arif, p. 566.