John Romer presents the history of the Byzantine Empire, the Roman state that outlived Rome itself and survived for a thousand years after the western half collapsed. He starts at the Hagia Sophia in Istanbul, the domed cathedral built under Justinian that still dominates the skyline of what was once Constantinople, and traces how the empire's wealth, bureaucracy, and Orthodox Christian faith held together a territory stretching across the eastern Mediterranean. Romer also travels to St. Mark's in Venice, where bronze horses and other treasures looted from Constantinople during the Fourth Crusade still sit on display, a reminder that much of Byzantium's material legacy now lives outside its own former capital. The film moves through the long line of emperors who ruled from Constantinople, the architecture that marked their power, and the slow military and political decline that ended with the city's fall to the Ottomans. Romer's case throughout is that this empire, often treated as a footnote to Rome, deserves to be understood on its own terms.