Bucellarii (the Latin plural of Bucellarius; literally "biscuit–eater",Greek: Βουκελλάριοι) is a term for a unit of soldiers in the late Roman and Byzantine empire, that were not supported by the state but rather by some individual such as a general or governor, in essence being his "household troops".
These units were generally quite small, but, especially during the many civil wars, they could grow to number several thousand men. In effect, the bucellarii were small private armies equipped and paid by wealthy influential people. As such they were quite often better trained and equipped, not to mention motivated, than the regular soldiers of the time. In the 6th century, Belisarius, during his wars on behalf of Justinian, employed as many as 7,000 bucellarii. By this time, the bucellarii were well integrated into the main Roman army, and soon the term came to be applied indiscriminately to well-equipped cavalry troops. Thus, in the 7th century, when the military recruitment areas formed the basis for the Theme system, one of the first themata was that of the Boukellariōn, in the area of Paphlagonia and Galatia, with its capital at Ankara.