In the late 3d cent. B.C., Roman law could no longer limit itself to the inhabitants of the republic but was forced to take account of the surrounding non-Roman peoples. Thus, to the jus civile, which governed relations among the Romans and those admitted to Roman status, was added the jus gentium, the law applied in dealings with a foreigner. The jus gentium incorporated much of the highly developed commercial law of the Greek city-states and of other maritime powers. Such provisions, being better adapted to Rome's expanding economic needs than the unyielding provisions of the jus civile, in time tended to be applied universally.
The development of new principles was especially vigorous after c.100 B.C., an important source being the jus honorarium, i.e., the law of the praetors (chief magistrates). On assuming office the praetor announced the principles, sometimes novel, that would govern his decisions. The praetors also contributed greatly to making practice more flexible. In place of the legis actiones, they often used the formulary system. A formula, like a legis actio, was a device for determining the issue between the parties; but instead of being a mere interchange of prescribed speeches, it provided a structure for discussing the actual dispute. Whichever method was used, when the nature of the dispute was agreed upon, the parties brought their case before the judex, a private functionary, who considered the evidence and gave judgment.