The Military Oath
Every Roman soldier pledged allegiance in a sacred oath, the sacramentum, that was recited on enlistment, annually on January 3, and also on the anniversary of the current emperor's reign:
"Step forward, recruit ["Lucius Junius Brutus"], and swear by the gods of Rome, the manes of your ancestors, and your own honor an unbreakable oath that you will follow your commander wherever he may lead you. You will obey orders enthusiastically and without question. You relinquish the protection of the Roman civil law and accept the power of your commander to put you to death without trial for disobedience or desertion. You promise to serve under the standards for your allotted time of duty and not to leave before your commander discharges you. You will serve Rome faithfully, even at the cost of your life, and will respect the law with regards to civilians and your comrades in camp. Congratulations. You are now a soldier of Rome!"
The soldiers also took a voluntary oath to defend each other, the ius iurandum:
"I swear that I will not leave my comrades for fear or for flight, and will not quit the ranks save to fetch or pick up a weapon, to strike an enemy, or to save a comrade!"
"Step forward, recruit ["Lucius Junius Brutus"], and swear by the gods of Rome, the manes of your ancestors, and your own honor an unbreakable oath that you will follow your commander wherever he may lead you. You will obey orders enthusiastically and without question. You relinquish the protection of the Roman civil law and accept the power of your commander to put you to death without trial for disobedience or desertion. You promise to serve under the standards for your allotted time of duty and not to leave before your commander discharges you. You will serve Rome faithfully, even at the cost of your life, and will respect the law with regards to civilians and your comrades in camp. Congratulations. You are now a soldier of Rome!"
The soldiers also took a voluntary oath to defend each other, the ius iurandum:
"I swear that I will not leave my comrades for fear or for flight, and will not quit the ranks save to fetch or pick up a weapon, to strike an enemy, or to save a comrade!"
Roman legion deployment - Late 1st century AD and 2nd-3rd centuries AD Click image to enlarge