Which Byzantine emperor is known for reconquering much of the territory previously ruled by Rome?

The Byzantine emperor known for reconquering much of the territory previously ruled by Rome is Justinian. He reigned from 527 to 565 AD and is most famous for his ambitious campaigns aimed at restoring the Roman Empire's former glory. Under Justinian's leadership, military commanders like Belisarius and Narses successfully retook significant parts of the former Roman territories in North Africa, Italy, and parts of the southern Mediterranean, including the city of Carthage and the Italian peninsula.

Justinian's efforts were not solely military; he also undertook sweeping legal reforms, codifying Roman law in a coherent body known as the "Corpus Juris Civilis," which has had a lasting influence on the legal systems of many countries. His reign is often seen as a high point of Byzantine culture and governance, leading to significant developments in art, architecture (such as the construction of the Hagia Sophia), and theology.

Other historical figures listed did not focus on reconquering territories on the same scale or had different principal legacies. For instance, Heraclius is known for his military campaigns against the Persians and the introduction of the term "Christian Empire," Constantine is notable for founding Constantinople and adopting Christianity, while Alexios established the