The history of the development of those rules and principles now considered in international law naturally falls into three periods, early, middle and modern.
The early period dates from the time of the development of early European civilization, and extends to the beginning of the Christian Era. During this period the germs of the present system appear.
The dispersion of the Greeks in many colonies which became practically independent communities gave rise to systems of intercourse involving the recognition of general obligations. The maritime law of Rhodes is an instance of the general acceptance of common principles. The main body of this law has not survived, yet the fragment appearing in the Digest, De Lege Rhodia de Jactu, is, after more than two thousand years, the basis of the present doctrine of jettison. It is reasonable to suppose that though the words of other portions of the Rhodian law are lost, the principles may have entered into formation of later compilations.
The recognition by Greece of the existence of other independent states, and the relations into which the states entered, developed crude forms of international comity, as in the sending and receiving of ambassadors and the formation of alliances.
Rome made many contributions to the principles of international law in the way of the extension of her own laws to wider spheres, and in the attempt to adapt Roman laws to conditions in remote territories. In this early period Rome may be said to have contributed to the field of what is now considered private international law rather than to that of public international law. This is evident in the laws in regard to marriage, contract, property, etc. The dominance of Rome impressed her laws on others, and extended the influence of those principles which, from general practice, or conformity to accepted standards, gained the name Jus Gentium.