TAXEShave been established as the base for the land tax under 'Umar I. The
region called the Sawad in the Sasanian period in Arabic literature is
either lower Iraq in general or is assumed to be identical with later
'Abbasi definitions. As we shall see, there was no administrative unit
in lower Iraq in the late Sasanian period that was exactly equivalent
to what was meant by the Sawad in the century following the Muslim
conquest. Consequently, the figures given for the taxes of the Sawad
in both periods are not subject to direct comparison. There are a
number of reasons why the land surveyed in the Sawad under 'Umar
I might be expected to have been less extensive than that claimed as
the base for the Sasanian land tax there. In the first place, by all
accounts the initial survey done by 'Uthman ibn I:Iunayf and I:Iud-
hayfa ibn al-Yaman was only in the Sawad of Kufa. Therefore, the
thirty-two to thirty-six million jartbs of land which they measured for
the land tax included neither the Sawad of Basra nor Hulwan.^97 Sec-
ond, the disastrous flooding of 628 took large tracts of land in lower
Iraq out of cultivation. Since much of it was in the district of Kaskar,
it may have been Sasanian crown land. However, the land reclaimed
by draining the swamps beginning in the time of Mu'awiya certainly
became either Muslim crown land or the private tithe land of the
developer and was consequently beyond the system of the unit of area
tax and was not reflected in the figures for the kharaj. Comparability
might also be affected by changes in crops such as the expansion of
rice-growing on land reclaimed from the swamps, which seems to have
been left untaxed or at least uncounted at first. Third, although the
Muslim survey covered cultivable land allowed to lie fallow, such land
was taxed at a lower rate. Following the conquest, a major population
shift took place in Iraq from the districts east of the middle Tigris to
the middle Euphrates and Shatt al-'Arab. This shift was accompanied
by a decline in agriculture east of the Tigris and an increase in agri-
culture around Basra, where the newly cultivated lands were state
domains, land grants to private persons, or tithe land.^98 On the other
hand, these factors, which tended to drive down the revenue from the
land tax, were offset by the increase in rates under the Muslims and
by their preference for collecting taxes in the heavier khusrawt(M.P.lAr.)
coins. Consequently, the taxes raised in the Sawad of Kufa by 'Uthman
ibn I:Iunayf, including the poll tax on five hundred thousand or five
97 Abii Yiisuf, Kharii;, pp. 69, 89.
98 Abii Yiisuf, Khariij, pp. 59-60; Ibn l:iawqal, $urat al-art;l, p. 239; IgakhrI, Kitiib
masiilik al-mamiilik (Leiden, 1927), p. 82.