The immunes were ancient Roman soldiers who possessed specialized skills.
They were exempt from the more tedious and dangerous tasks other soldiers were required to do, such as ditch digging and rampart patrol.
[1] Prior to becoming an immunis, men were required to serve as miles gregarius (also known as munifex), a non-specialist regular soldier.
[2] The discens received the same basic pay and board as the non-specialists until he qualified for immunis status.
[3] Engineers, artillerymen, musicians, drill and weapons instructors, military police, carpenters, hunters and medical staff were among the multiple specialized jobs immunes provided for the Roman army.