(from stare, 'to stand at someone's side'; in the military realm = ordinance). Soldiers who in the Imperial Period belonged to the staff of military commanders and governors with troops. They could belong to the troops from the city of Rome or to those in the provinces. Their tasks are difficult to determine; they might have functioned as letter couriers and prison wards. However, these tasks were probably only an (occasional) part of their duties.
Bibliography
R. Haensch, A commentariis und commentariensis, in: Y. Le Bohec (ed.), La hiérarchie…