The Codex Theodosianus (Eng. Theodosian Code) was a compilation of the laws of the Roman Empire under the Christian emperors since 312. A commission was established by Theodosius II and his co-emperor Valentinian III on 26 March 429 and the compilation was published by a constitution of 15 February 438. It went into force in the eastern and western parts of the empire on 1 January 439.
On March 26, 429, Emperor Theodosius II announced to the senate of Constantinople his intentions to form a committee to codify all of the laws (leges, singular lex) from the reign of Constantine up to Theodosius II and Valentinian III. Twenty-two scholars, working in two teams, worked for nine years starting in 429 to assemble what was to become the Theodosian Code. The chief overseer of the work was Antiochus Chuzon, a lawyer and a Prefect and Consul from Antioch.
Their product was a collection of 16 books containing more than 2,500 constitutions issued between 313 and 437. John F. Matthews illustrates the importance of Theodosius' Code when he said, "the Theodosian Code was the first occasion since the Twelve Tables on which a Roman government had attempted by public authority to collect and publish its leges." The code covers political, socioeconomic, cultural and religious subjects of the 4th and 5th century in the Roman Empire.
A collection of imperial enactments called the Codex Gregorianus had been written in c. 291-4 and the Codex Hermogenianus, a limited collection of rescripts from c. 295, was published. Theodosius desired to create a code that would provide much greater insight into law during the later Empire (321-429). According to Peter Stein, "Theodosius was perturbed at the low state of legal skill in his empire of the East." He apparently started a school of law at Constantinople. In 429 he assigned a commission to collect all imperial constitutions since the time of Constantine. The laws in the code span from 312-438, so by 438 the "volume of imperial law had become unmanageable".
During the process of gathering the vast amount of material, often editors would have multiple copies of the same law. In addition to this, the source material the editors were drawing upon changed over time. Clifford Ando notes that according to Matthews, the editors "displayed a reliance on western provincial sources through the late 4th century and on central, eastern archives thereafter."