Similar to the earlier groundbreaking Eastern Front (1941) in terms of display and general gameplay,[2] Legionnaire added a real-time computer opponent, and is one of the earliest examples of a real-time tactics (RTT) game[citation needed].

The player took the side of the Romans, playing the role of Caesar, giving orders to their forces in real time. The computer played the barbarians, in blue, with the player's legions in pink. There were three types of units; infantry was represented by a sword, cavalry as a horse head, and Caesar's own Imperial Guard as an eagle.[3] Orders were given to the units by moving a cursor over them with the joystick and then holding down the joystick button; existing commands would be displayed as a moving arrow, and new orders could be entered by pressing the joystick in the four cardinal directions.