When the centre of the Empire was moved to the Greek East in the 4th century, many legal concepts of Greek origin appeared in the official Roman legislation. The influence is visible even in the law of persons or of the family, which is traditionally the part of the law that changes least. For example, Constantine started putting restrictions on the ancient Roman concept of patria potestas, the power held by the male head of a family over his descendents, by acknowledging that persons in potestate, the descendents, could have proprietary rights. He was apparently making concessions to the much stricter concept of paternal authority under Greek-Hellenistic law. The Codex Theodosianus (438 AD) was a codification of Constantian laws. Later emperors went even further, until Justinian finally decreed that a child in potestate became owner of everything it acquired, except when it acquired something from its father.
The codes of Justinian, particularly the Corpus Juris Civilis (529-534) continued to be the basis of legal practice in the Empire throughout its so-called Byzantine history. Leo III the Isaurian issued a new code, the Ecloga, in the early 8th century. In the 9th century, the emperors Basil I and Leo VI the Wise commissioned a combined translation of the Code and the Digest, parts of Justinian's codes, into Greek, which became known as the Basilica. Roman law as preserved in the codes of Justinian and in the Basilica remained the basis of legal practice in Greece and in the courts of the Eastern Orthodox Church even after the fall of the Byzantine Empire and the conquest by the Turks, and also formed the basis for much of the Fetha Negest, which remained in force in Ethiopia until 1931.
According to Ralph of Coggeshall, Henry the Young King instigated rebellion against Henry II; he wanted to reign independently over at least part of the territory his father had promised him, and to break away from his dependence on Henry II, who controlled the purse strings. There were rumors that Eleanor might have encouraged her sons to revolt against their father.
Henry the Young King abandoned his father and left for the French court, seeking the protection of Louis VII; his younger brothers, Richard and Geoffrey, soon followed him, while the five-year-old John remained in England. Louis gave his support to the three sons and even knighted Richard, tying them together through vassalage. Jordan Fantosme, a contemporary poet, described the rebellion as a "war without love".
The three brothers made an oath at the French court that they would not make terms with Henry II without the consent of Louis VII and the French barons. With the support of Louis, Henry the Young King attracted many barons to his cause through promises of land and money; one such baron was Philip, Count of Flanders, who was promised 1,000 and several castles. The brothers also had supporters ready to rise up in England. Robert de Beaumont, 3rd Earl of Leicester, joined forces with Hugh Bigod, 1st Earl of Norfolk, Hugh de Kevelioc, 5th Earl of Chester, and William I of Scotland for a rebellion in Suffolk. The alliance with Louis was initially successful, and by July 1173 the rebels were besieging Aumale, Neuf-March, and Verneuil, and Hugh de Kevelioc had captured Dol in Brittany. Richard went to Poitou and raised the barons who were loyal to himself and his mother in rebellion against his father. Eleanor was captured, so Richard was left to lead his campaign against Henry II's supporters in Aquitaine on his own. He marched to take La Rochelle but was rejected by the inhabitants; he withdrew to the city of Saintes, which he established as a base of operations.
In the meantime Henry II had raised a very expensive army of more than 20,000 mercenaries with which to face the rebellion. He marched on Verneuil, and Louis retreated from his forces. The army proceeded to recapture Dol and subdued Brittany. At this point Henry II made an offer of peace to his sons; on the advice of Louis the offer was refused. Henry II's forces took Saintes by surprise and captured much of its garrison, although Richard was able to escape with a small group of soldiers. He took refuge in Chteau de Taillebourg for the rest of the war. Henry the Young King and the Count of Flanders planned to land in England to assist the rebellion led by the Earl of Leicester. Anticipating this, Henry II returned to England with 500 soldiers and his prisoners (including Eleanor and his sons' wives and fiances), but on his arrival found out that the rebellion had already collapsed. William I of Scotland and Hugh Bigod were captured on 13 and 25 July respectively. Henry II returned to France and raised the siege of Rouen, where Louis VII had been joined by Henry the Young King after abandoning his plan to invade England. Louis was defeated and a peace treaty was signed in September 1174, the Treaty of Montlouis.
When Henry II and Louis VII made a truce on 8 September 1174, its terms specifically excluded Richard. Abandoned by Louis and wary of facing his father's army in battle, Richard went to Henry II's court at Poitiers on 23 September and begged for forgiveness, weeping and falling at the feet of Henry, who gave Richard the kiss of peace. Several days later, Richard's brothers joined him in seeking reconciliation with their father. The terms the three brothers accepted were less generous than those they had been offered earlier in the conflict (when Richard was offered four castles in Aquitaine and half of the income from the duchy): Richard was given control of two castles in Poitou and half the income of Aquitaine; Henry the Young King was given two castles in Normandy; and Geoffrey was permitted half of Brittany. Eleanor remained Henry II's prisoner until his death, partly as insurance for Richard's good behaviour.