The Roman Empire was an empire of Antiquity that lasted from the accession of Augustus Caesar in 27 BC to the sack of Rome in 476 AD, although the Byzantine Empire survived until 1453. It was centered on the city of Rome on the Italian Peninsula. The Roman Empire controlled most of the areas surrounding the Mediterranean, as well as Gaul, parts of Germania, and Britannia. The Romans left a legacy of the Roman law code, the Latin language, and the spread of Christianity throughout Europe.
The transition between the Roman Republic and the Empire, occurring in the late 1st century BC, was a gradual process without a clear beginning or end. However, the conventional foundation date is 27 BC, when Octavian assumed the title Augustus Caesar. Previous to that, Octavian had fought a civil war against Mark Antony and Cleopatra and decisively defeated them at the Battle of Actium.
The 1st century AD saw a string of successful emperors, including Augustus, Vespasian, and Tiberius, as well as several unpopular ones, such as Nero and Caligula. In 117, during the reign of Trajan, the Empire reached its greatest extent with the temporary incorporation of lands in Britannia and the Middle East. Christianity also won many followers in this period, although Roman paganism remained the official and dominant religion.
Roman dominance began to wane in the 2nd century, and during the 3rd century the Empire almost dissolved. As more and more citizens converted to Christianity, official persecution of the religion became unpopular. Roman paganism was defended by the philosopher-emperor Marcus Aurelius, known more for his writing than his leadership. After several splits, the Empire was strengthened by the reign of Diocletian in the late 3rd century, averting complete collapse. In 313, the Edict of Milan legalized practice of Christianity, a major step for the nascent religion.
In 330, Constantine the Great declared Christianity as the official religion of the Empire. This date is also the one typically assigned to the beginning of the Eastern Roman Empire as an entirely independent entity. Splitting the Empire doomed the West to fall but allowed the East to last for nearly another millennium. The Western Roman Empire struggled on through the 4th century, surviving invasions by various Germanic tribes as well as the Huns.
The city of Rome was sacked several times in the 5th century, by various groups including the Vandals and Visigoths. Roman Britain was abandoned in 410 and by the 450s the northern border had entirely collapsed. On 476, the last Roman Emperor, Romulus Augustus, was deposed by Odoacer, who took the title Rex Italia instead of Emperor. The Domain of Soissons in northern France held out until 486, while the Byzantine Empire in the East survived until 1453. However, 476 is generally agreed to be the end of the Western Roman Empire.
The Roman Empire at its maximum extent encompassed nearly all of the territory surrounding the Mediterranean Sea as well as additional lands in Europe and the Middle East. All of France (then known as Gaul), England and Wales, parts of southern and western Germany, most of Switzerland and southern Austria, much of Romania and Bulgaria, Anatolia, and the Levant were also under Roman control.