ife, whose adherents spoke of
themselves as citizens of the world, had fastened upon the old
antithesis of law (or convention) and nature, and formed the conception
of a law of nature, which should have a reasonable basis and a validity
superior to the arbitrariness of the city law. To this ideal conception
the Roman law of the men of all nations gave a body and a reality.
Stoicism became the 'established' philosophy of Rome, and Roman lawyers
well-nigh identified the '_ius gentium_' with the ideal law of nature,
describing it as that which natural reason has established among all
men. Yet for at least one of the great classical lawyers, whose words
have been enshrined in Justinian's legislation, the identification was
incomplete. By nature, it was said, all men are free, and mankind has
departed from what natural reason requires, in permitting slavery. Thus
the law of nature must be sought in something more universal than the
practice of mankind. More than fifteen hundred years later in an English
court an argument against the recognition of the rights of a slave-owner
was successfully founded on the law of nature.

Before the Roman law had been put (at Constantinople) into the final
shape in which it is preserved to us, the Roman empire in the west had
already been broken up by barbarian invasions. The invaders brought with
them their tribal laws and customs, rude, often cruel, narrow rather
than simple, for simplicity is the work of civilization. They did not
understand, and could not adopt, the law of the world into which they
had come. Yet neither could they, if they would, force their laws upon
the conquered inhabitants. Among these the old civilization lingered on
in a degenerate form, and with it the Roman law. One of the first things
that happened was that the conquerors drew up for their Roman subjects
short codes of the Roman law as it survived in a debased form, as they
drew up statements of their own law for their followers. For a long time
each man, according to the community to which he belonged, had a
'personal' law. As late as A.D. 850 we hear that in France it might
happen that five men met together and each would have a different law.
Of course such a state of things means before very long that there must
be at any rate one set of common legal rules which must be applied
throughout a territory, namely rules to decide which kind of personal
law is to be used when there is a dispute between two persons w