The Western Roman Empire refers to the western half of the Roman Empire, from its division in 395. The other half of the Roman Empire became known as the Eastern Roman Empire, today widely known as the Byzantine Empire. The capital of the Western Roman Empire was in Milan, until it was moved to Ravenna in 402.
The Western Empire existed intermittently in several periods between the 3rd century and 5th century, after Diocletian's Tetrarchy and the reunifications associated with Constantine the Great and Julian the Apostate. Theodosius I was the last Roman Emperor who ruled over a unified Roman empire. After his death in 395, the Roman Empire was permanently divided. The Western Roman Empire ended officially with the abdication of Romulus Augustus under pressure of Odoacer on 4 September 476, and unofficially with the death of Julius Nepos in 480.
Despite a brief period of reconquest by its counterpart, the Eastern Roman Empire, the Western Roman Empire would not rise again. As the Western Roman Empire fell, a new era began in Western European history: the Middle Ages.