Alesia was the capital of the Mandubii, one of the Gallic tribes allied with the Aedui. The Celtic oppidum was conquered by Julius Caesar during the Gallic Wars and afterwards became a Gallo-Roman town. Modern understanding of its location was controversial for a long time; however, it is now thought to have been located on Mont-Auxois, near Alise-Sainte-Reine in Burgundy, France.

An oppidum is a large fortified Iron Age settlement or town. Oppida are primarily associated with the Celtic late La Tène culture, emerging during the 2nd and 1st centuries BC, spread across Europe, stretching from Britain and Iberia in the west to the edge of the Hungarian plain in the east. These settlements continued to be used until the Romans conquered Southern and Western Europe. Many subsequently became Roman-era towns and cities, whilst others were abandoned. In regions north of the rivers Danube and Rhine, such as most of Germania, where the populations remained independent from Rome, oppida continued to be used into the 1st century AD.