Oddly, Gaius is known only by this common Roman first name.

A Roman, and Roman law teacher and sometime lawyer – a jurist - who was one of many experts on Roman law in the centuries preceding Justinian. His origins are unclear but historians believe that he lived in Rome for a time where he began to write on the Roman law.

Holland wrote:

"His fame was doubtless, rather that of a teacher than of a practising lawyer, and his (Roman law) manuals became the received textbooks in the regular course of legal study."

But contrary to his contemporaries, including Ulpian (who came a hundred years later, Gaius gained the ultimate fame of having his treatises Everyday Law and his own version of a Roman Law Institutes selected by Justinian’s law reform team for much of the structure and content of the all-important Corpus Juris Civilis and its Institutes.

GaiusEven before that, Roman Emperor Theodosius II (347-395) had named him as one of five jurists the writings of which Roman law judges had to follow (Ulpian was also selected).

He published, at last count, some fifteen books, the most important of which was his Institutions, discovered by archeologist Niebuhr at Verona in 1816.

It was than that historians could confirm the profound incorporation of his Roman law theories into Justinian’s Institutes, which became the definitive work of law in Europe for a thousand years. Of the 901 articles of Justinian’s Institute, almost half were taken from Gaius, as was the general organization plan of Justinian’s work.

Justinian and his reform team was so fond of him, that they referred to him in the Institutes as Gaius noster or "our own Gaius" and he is the only Roman law jurist – other than Tribonian and the othr reform team members, to be named in the preamble of Justinian’s Institutes published on November 21, 533.

But jealousy seemed to affect Ulpian and Paulus, both of whom were fully aware of Gaius' theories yet never once cited his work. Of course, as between themselves, Ulpian and Pau never cited each other either.

But Gaius was recognized in the Law of Citations as one of the great Roman jurists.

Even today, Gaius' writings are still studied by students at civil law universities and are the subject of ongoing seminars.