When Rome fell in 476 CE, its eastern half continued for nearly a thousand more years. The Byzantine Empire, centered on Constantinople, preserved Roman law, Greek culture, and Christian tradition while the West descended into fragmentation.
At its height under Justinian I (527-565 CE), the empire reconquered much of the western Mediterranean. Justinian's legal code, the Corpus Juris Civilis, would later form the foundation of law in much of Europe. His wife Theodora, a former actress, became one of history's most powerful empresses.
Constantinople itself was a marvel—the largest city in Christendom for centuries. Its walls withstood numerous sieges, and its location controlling the Bosphorus made it a commercial crossroads between Europe and Asia.