The Battle of Alesia or Siege of Alesia takes place in September, 52 BCE around the Gallic oppidum of Alesia, a major town center and hill fort of the Mandubii tribe.

It is fought by an army of the Roman Republic commanded by Julius Caesar, aided by cavalry commanders Mark Antony, Titus Labienus and Gaius Trebonius, against a confederation of Gallic tribes united under the leadership of Vercingetorix of the Arverni.

It is the last major engagement between Gauls and Romans, marking the turning point of the Gallic Wars in favor of Rome.

The Siege of Alesia is considered one of Caesar's greatest military achievements and a classic example of siege warfare and investment.

The battle of Alesia can safely be described as marking the end of Celtic dominance in France, Belgium, Switzerland and Northern Italy.The battle site is probably atop Mont Auxois, above modern Alise-Sainte-Reine in France, but this location, some have argued, does not fit Caesar's description of the battle.

A number of alternatives have been proposed over time, among which only Chaux-des-Crotenay (in Jura in modern France) remains a challenger today.

At one point in the battle, the Romans are outnumbered by the Gauls by four to one.

The event is described by several contemporary authors, including Caesar himself in his Commentarii de Bello Gallico.

After the Roman victory, Gaul (very roughly modern France) is subdued and becomes a Roman province.

The refusal of the Roman senate to allow Caesar the honor of a triumph for his victory in the Gallic Wars eventually lead, in part, to the Roman Civil War of 49–45 BCE.