According to Roman tradition, popular pressure led to the appointment for 451 bce of ten men with consular imperium, for writing down statutes, legibus scribundis, in order to put an end to the patrician and priestly monopoly of the law (see decemvirates, first and second). They compiled ten tables, were reappointed for 450 bce, and compiled two more, including the ban on intermarriage between patricians and plebeians, which was rapidly abrogated by the lex Canuleia of 445 bce. An attempt to remain in office for 449 bce also failed. The fundamental consequence was that customary law was now enacted by statute and given legislative basis; and the Twelve Tables were seen as the starting-point of the development of Roman law.
We have no way of verifying this tradition; and it may be that the impetus came rather from a desire for self-regulation within the élite. But the legal, antiquarian, oratorical, and historical tradition preserves a remarkably consistent view of the content of the Twelve Tables, even if the language has been modernized. And it is reasonably certain both that they underlay the colonial charters of the late 4th cent. bce onwards and that legislation to revise them began in the early 3rd cent. bce.
Three points remain controversial: there is little evidence for the order of the different provisions and modern editions largely classify them perforce according to the later divisions of the law; it is uncertain how complete is the record preserved by our sources; and it is disputed how far they contained what was later regarded as public law. Our knowledge of the order depends on the fragments of the commentary by Gaius(2) quoted in the Digest and on the occasional attribution of particular provisions to particular tables; but it is at least certain that the provision conventionally printed as Tabula I, 1, is the first. As far as the second point is concerned, there seem to be few areas of the private law of the late republic where a provision of the Twelve Tables is not at some point invoked and it is unlikely that whole fields covered by the Twelve Tables have disappeared without trace. And if one thinks in less rigid terms about the third problem, a consistent view of our tradition must lead to the conclusion that even if the Twelve Tables mostly concerned themselves with relations between individuals, they also at times concerned themselves with relations between individuals and the community.
The Twelve Tables were presumably not much systematized and perhaps put together largely from material which was readily to hand and which the ten men supposed to be actually or potentially useful, not unlike the later praetor's edict. It would be exaggerated to describe the Twelve Tables as a code. They attracted commentary from the middle republic onwards, but gradually became more and more obsolete as the praetor's edict developed, becoming progressively the province of antiquarians.