American Tract Society Bible Dictionary
A detachment or division consisting of four men, Mal 12:4 . The Romans detached a quarternion of four men for a night guard and divided the night into four watches, so that each soldier should in his turn be on guard three hours. (See HOURS.)\par When therefore Herod, who adopted the Roman customs, is said to have delivered Peter to four quaternions of soldiers, it is to be understood that he was guarded by four men at a time, namely, two in the prison with him, and two before the doors, and that they were relieved every three hours by four others; making in all sixteen men.\par