Herennius Modestinus in the context of "Alexander Severus"

Gaius (/ˈɡeɪəs/; fl. AD 130–180) was a Roman jurist. Little is known about his personal life, including his name (Gaius or Caius being merely his personal name or praenomen). It is also difficult to ascertain the span of his life, but it is assumed he lived from AD 130 to at least AD 179, as he wrote on legislation passed within that time.

From internal evidence in his works it may be gathered that he flourished in the reigns of the emperors Hadrian, Antoninus Pius, Marcus Aurelius and Commodus. His works were thus composed between the years 130 and 180. After his death, however, his writings were recognized as of great authority, and the emperor Theodosius II named him in the Law of Citations, along with Papinian, Ulpian, Modestinus and Paulus, as one of the five jurists whose opinions were to be followed by judicial officers in deciding cases. The works of these jurists accordingly became most important sources of Roman law.

Byzantine law was essentially a continuation of Roman law with increased Orthodox Christian and Hellenistic influence. Most sources define Byzantine law as the Roman legal traditions starting after the reign of Justinian I in the 6th century and ending with the Fall of Constantinople in the 15th century. Although future Byzantine codes and constitutions derived largely from Justinian's Corpus Juris Civilis, their main objectives were idealistic and ceremonial rather than practical. Following Hellenistic and Near-Eastern political systems, legislations were tools to idealize and display the sacred role and responsibility of the emperor as the holy monarch chosen by God and the incarnation of law "nómos émpsychos", thus having philosophical and religious purposes that idealized perfect Byzantine kingship.

Though during and after the European Renaissance Western legal practices were heavily influenced by Justinian's Code (the Corpus Juris Civilis) and Roman law during classical times, Byzantine law nevertheless had substantial influence on Western traditions during the Middle Ages and after.