Roman Empire

The Roman Empire began when Octavian (Augustus) became Rome's first emperor in 27 BC, ending nearly five centuries of republican government following Julius Caesar's assassination and the civil wars that followed it. At its territorial height under Trajan (around 117 AD), it controlled roughly 2 million square miles spanning Britain, continental Europe to the Rhine and Danube, the entire Mediterranean coastline, and the Near East. It split into Western and Eastern halves in 285 AD under Diocletian for administrative reasons; the Western Empire fell in 476 AD, while the Eastern half — commonly called the Byzantine Empire by historians, though its own citizens still called themselves Roman — continued for nearly another thousand years until Constantinople fell in 1453.