The Roman Empire ruled the Mediterranean and much of Europe, Western Asia and North Africa. The Romans conquered most of this during the Republic, and it was ruled by emperors following Octavian's assumption of effective sole rule in 27 BC. The western empire collapsed in 476 AD, but the eastern empire lasted until the fall of Constantinople in 1453.

Throughout its history, the Roman Empire and Republic played a pivotal role in civilizing the known world, shaping the course of Western civilization. From its early days as a small city-state, Rome expanded its influence through conquest, diplomacy, and cultural assimilation, spreading its advanced legal systems, architectural innovations, and societal structures across vast territories.