Ancient Rome was a civilization that grew from a small agricultural community founded on the Italian Peninsula in the 9th century BC to a large empire straddling the Mediterranean Sea. In its twelve centuries of existence, Roman civilization shifted from a monarchy, to a republic based on a combination of oligarchy and democracy, to an increasingly autocratic empire. It came to dominate Western Europe and the area surrounding the Mediterranean Sea through conquest and assimilation.

The Roman empire went into decline in the 5th century AD. Plagued by internal instability and attacked by various migrating peoples, the western part of the empire, including Hispania, Gaul, and Italy, broke up into independent kingdoms in the 5th century. The eastern part of the empire, governed from Constantinople, survived this crisis, and would live on for another millennium, until its last remains were finally annexed by the emerging Ottoman Empire. This eastern, medieval stage of the Empire is usually referred to as the Byzantine Empire by historians.

Roman civilization is often grouped into "classical antiquity" with ancient Greece, a civilization that inspired much of the culture of ancient Rome. Ancient Rome contributed greatly to the development of law, war, art, literature, architecture, technology and language in the Western world, and its history continues to have a major influence on the world today.