Bucellarii (the Latin plural of Bucellarius; literally "biscuit–eater", Greek: Βουκελλάριοι) were formations of escort troops used in the Roman Empire in Late Antiquity. They were employed by high-ranking military figures (such as Flavius Aetius and Belisarius) or civil office-holders. Their name is derived from the type of bread rations eaten by these troops, so-called buccellatum. The term bucellarii came into common use during the reign of Emperor Honorius (r. 395–423).
According to Jon Coulston, one bucellarii regiment is attested in the Notitia Dignitatum. The creation of the bucellarii reflected an increase in the "use of armed retinues by public officials" in the Roman Empire. These armies were, therefore, associated with the decline of imperial authority because they demonstrated that it no longer had the monopoly of violence. The bucellarius had close ties with its commander, supporting him in his quarrel with other commanders and even against the Empire, court, and emperor. This is shown by the army of Heraclian, which was used in his attempt to seize Roman Italy from Emperor Honorius.