The Romans, even before their conquest of Greece, had recognised the distinction between the law applicable to themselves exclusively and that what they had in common with other nations. To the former they gave the name jus civil, and the latter they called jus gentium.
The distinction assumed greater importance as the Romans came more into contact with foreigners. They found that the jus gonium being common to all nations had its foundation in conformity with universal reasons and justice.
The progressive liberalisation of the law during the Republican period extended the scopc of jus gentium. The Romans looked upon jus gentian as a concrete embodiment of the law of nature. This similarity of features between the jus gonium and the just naturals brought about almost a complete identification of the two.
Natural law has played an important part in the development of modern jurisprudence by rationalising or moralising law. It is desirable that law and morality should have a close connection.
There should be recognition of the principles of natural justice in almost every system of law. The view of Hobbes that natural law was merely general rules of precepts discovered by man by virtue of his reasoning powers and faculty of observation found favour with Hugo Grotius.
The development of equity in Rome and England was mainly designed to modify the rigour of the law in its application to individual cases. In course of time in an attempt to translate into practice the ideals of justice and morality it evolved definite rules, founded on distinct principles, that existed by the side of the original civil law for a considerable length of time until its superiority was recognised and it was made a part and parcel of the ordinary law of the land.