The Battle of Alesia or Siege of Alesia was a military engagement in the Gallic Wars around the Gallic oppidum (fortified settlement) of Alesia, a major centre of the Mandubii tribe. It was the last major engagement between Gauls and Romans, and is considered one of Caesar's greatest military achievements and a classic example of siege warfare and investment; the Roman army built dual lines of fortifications—an inner wall to keep the besieged Gauls in, and an outer wall to keep the Gallic relief force out. The Battle of Alesia marked the end of Gallic independence in modern day territory of France and Belgium.

With the revolt crushed, Caesar set his legions to winter across the lands of the defeated tribes to prevent further rebellion. Troops were also sent to the Remi, who had been steadfast allies to the Romans throughout the campaign. But resistance was not entirely over: southwest Gaul had not yet been pacified. Alesia proved to be the end of generalized and organized resistance against Caesar's invasion of Gaul and effectively marked the end of the Gallic Wars. In the next year (50 BCE) there were mopping-up operations. During the Roman civil wars Gallia was essentially left on its own.