It is difficult to provide a comprehensive and finite list of the sources of Roman law, since the Roman jurists never defined the term 'source of law' and different sources were emphasized at certain periods in the history of the Roman legal system to reflect their prominence as instruments of legal reform.

There are three state­ments in which the sources of Roman law are listed, seemingly without any specific order. The earliest is by Cicero (Topica 5.28) in the first century BC. The second is a comment by the second-century jurist Gaius in his Institutes (Inst.Gai.1.1.-7.).

The latter was adopted and amended in Justinian's Institutes of the sixth century AD (Inst.1.2.). All three list legislation (laws and plebiscites), resolutions of the Senate, and edicts of the magistrates as sources of law. Apart from these, Cicero also mentions equity, custom, and decided cases in his list of sources. This has puzzled modern scholars, since some of these 'sources' are not included in the statements by Gaius and the drafters of Justinian's Institutes. In an attempt to explain this inconsistency, Robinson (Sources, 25-9) has shown that Cicero's account of the sources of Roman law had a rhetorical purpose as weapons in the arsenal of the Roman advocate, whereas the two later comments by Gaius and the drafters of Justinian's Institutes merely listed the sources of both the ins civile and the ius gentium. Gaius added imperial enactments to his list since the legislative activities of the emperor were fast becoming a prominent source of law during the second century. The Institutes of Justinian adopted Gaius' list of sources and restored custom as a source of law. Robinson has demonstrated (Sources, 29), however, that custom had a different meaning by the sixth century AD. Cicero understood 'custom' as ancestral tradi­tion (mos maiorum) in the context of the ius civile, while the term custom in the Institutes of Justinian referred to local and regional variations on the law of the Roman Empire.

For a good recent account, see Ibbetson, D., 'Sources of Law from the Republic to the Dominate', in Cambridge Companion, 25-44.

2.1

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