ADMINISTRATIONcations of Sasanian institutions and practices which were based on the
principles underlying Sasanian usages and took the form of increased
regularity, uniformity, and theoretical refinement. This was the case
in the extension of the unit of area system of assessing taxes to groves
of palm and fruit trees, in the definition of taxes in kind as provisions
for the army, and in the extension of exemptions from the poll tax to
everyone too old or infirm to pay it, or to those employed in state
service, to members of the religion of the rulers, or to those following
a religious profession. Thus, while the main aspects of the poll tax
already existed under the Sasanians, it received its characteristic Islamic
form of a tax on the economically productive parts of society whose
religion was different from that of the rulers in return for military
protection. This happened in Iraq because of the nature of the Muslim
occupation as both a ruling religious community and a military gar-
rison. These religious and military dimensions to the poll tax in the
late Sas ani an period tended to be reinforced by the Arab-Muslim
concept of jizya and led ultimately to the Islamic distinction between
land and poll taxes in both practice and theory. This kind of change,
which was really a matter of the continuing development of tendencies
in the late Sasanian period catalyzed by the Muslim conquest, may
also be seen in the way the relationship between taxation and justice
under the Sasanians was reinforced by Islamic values and by practical
circumstances.
In addition to the details or tax administration, one of the most
significant results of this study so far is to suggest a continuity of
ideological development in administrative theory. Although principle
did not necessarily correspond to practice as we have seen, theory was
related to and responsible for certain institutional arrangements. How-
ever, the problems encountered in evaluating the amount of taxes
collected under the Sasanians and Muslims make it necessary to define
and compare the geographical administrative units under both regimes.