This ‘law of the men of all nations’ (ius gentium) was of course not an international law, it was a law administered by Roman officers, and it was coloured by Roman conceptions, however much it may have drawn from a comparison of foreign laws with which the Romans were brought into contact.  In turn it reacted upon the more narrow law of Roman citizens (ius civile), broadening its conceptions and enabling it to free itself from primitive formalism.  It also made easier the task of Roman governors who were called upon to administer the various laws of the different countries which came to form the Roman empire.

The gradual extension of the citizenship (completed at the end of the second century A.D.) to the whole of the inhabitants of the empire made possible, at least in outward appearance, the application of a uniform system of law throughout what was then the civilized world, though beneath an apparent uniformity local traditions and customs survived to the end, at any rate in the east.  The ‘civil law’, as the Roman law in its final form has been called down to the present day, consists of elements of the narrowly Roman and the more universal law inextricably interlaced.

This Roman solution of the problem of the foreign litigant is of much more than merely practical importance.  The Stoic philosophy which grew up amid the decay of the old city life, 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