Quote Originally Posted by Mad Guitar Murphy
Hmm, I'm not sure an institution like patria potestas is still very relevant in western law:)
I must admit I don't remember a lot of the content of the 12 tables. Didn't they contain the traditio symbolica and basic stuff like that? I'd say it is pretty crucial for a society to function.

Are you refering to imperial edicts from 117 AD onwards? Because I think the compilatores, the legislators responsible for the Institutiones, used imperial edicts from 117 AD (Hadrian) onwards for the codification. I agree it is beyond doubt at least Tribonianus, who was in charge of the lawmaking operation, was very fond of classical lawyers from Hadrian onwards.
I'm merely using patria potestas to point out that not everything in law was in the twelve tablets. The tablets themselves contained, three tablets about court procedure, one tablet each for family, inheritance and tutorship, and propriety and neigbourly relations, two for crimes, one for sacral law, and two tablets of corrections and expansions.

Otherwise, from the 39 authors quoted in the Digestae, only 4 or 5 are not from the classical period (that is, the principate, legal science considers that the classical preiod of Roman law). Institutiones were mostly merely reworked Institutiones written by Gaius around 160 AD. The Codex Iustinianus (and the later Novellae) contains imperial edicts that were still, at that time, active, legally (possibly taken from the Codex Theodosianus, which contained constitutions from Hadrian onward). The Institutiones were merely a work whose purpose was to serve in the education of new lawyers (at that time, there were law schools in Constantinople and Beryt, as well as Alexandria and a couple of other places).

As far as things go, it was Justinian himself who ordered Tribonian and the other members of the groups (different groups worked on different works, but Tribonian was in all, except for the Novellae, as he died before their creation) to use classical authors, mainly because at that time the Roman Empire reached the height of legal development, as well as economic and cultural.