Keeping Kings in Check 73the same spirit, the ius commune was a law that was common to the whole of
Catholic Europe— but especially to the most developed part of that region,
which was Italy. As such, it was contrasted to the ius propria, the law of any
par tic u lar jurisdiction.
Two bodies of law contributed to the making of the ius commune. One
was Roman law, which was rediscovered by Western Eu ro pe ans in the elev-
enth century, when the full text of Justinian’s Digest came to the attention of
scholars. Th e other main source was the canon law of the Catholic Church—
which itself was strongly infl uenced by Roman law while (broadly speaking)
placing a greater stress on substantive principles than on specifi c rules and
formalities.
If natural law and the ius gentium found their principal expressions in the
writings of scholars (meaning theologians and phi los o phers), then the ius
commune was the province of practicing lawyers and judges, whose task was
to apply these general principles to the myriad problems of human social
life. Th ey did this chiefl y in consilia, which were rec ords of court proceed-
ings and judgments or opinions of lawyers on specifi c issues put to them.
Th ese writings were, in the aggregate, enormously greater in bulk than the
various expositions of natural law. Th ey have been, however, much less ac-
cessible to later scholars, since they were diff used throughout the chanceries
and archives of Eu rope. For this reason, the impact of the ius commune on
the later development of international law has been underappreciated (and
continues to await a full treatment).
It is, however, apparent that many of the principles employed by later writ-
ers in the natural- law tradition actually came from this source rather than
from the actual natural- law writing of the Middle Ages. Moreover, within the
ius commune, the canon law contribution to international law has been espe-
cially overlooked. Doctrines about papal superiority over secular rulers, for
example, were of canon- law origin. Much of diplomatic law and practice, too,
arose out of church practices, and hence out of canon law. So did many of
the specifi c rules that were devised concerning the conduct of war.
At the same time, though, it should be borne in mind that natural law
(a nd t he ius gentium along with it) was, in principle, more cosmopolitan
than the ius commune, because it was applicable to, literally, the whole hu-
man race without any distinction as to culture, history, or religion. Th e ius
commune, in contrast, although it was a transnational law, was nevertheless