The Eastern Roman Empire (The Byzantine Empire) was small after the barbarians took over the land. The Byzantine Empire was Constantinople and a little bit of land around the Aegean Sea. Then Justinian, the Emperor, made it bigger.
Justinian was the son of farmers. When he grew up, he did not want to be a farmer. He asked his parents if he could go to Constantinople and live with his uncle Justin, commander of the palace guard. His parents said, "OK." He went on a long adventure to Constantinople. When he got there he went to school. School was tough for him. He helped his uncle then his uncle became Emperor. His uncle adopted him because he really liked him. Justinian's uncle died so Justinian became emperor.
Justinian wanted to take back the Roman Empire. Was he successful? Yes, he was. Justinian had a problem. People had different laws in each part of the Empire. Justinian made a set of laws that everyone had to follow. He called the laws The Code of Justinian.