Sapper is a relatively modern term, derived from the trenches or "saps" driven towards the walls of besieged forts or towns during the age of black powder war. Ancient engineers would be considered almost a form of magician, and have titles derived from their specialty. The Latin term was ingenium, which could be translated as "a man who's clever with tools and mechanisms". His assistants would be considered "Immunes", since their special skills would exempt them from ditch digging and other routine tasks.
Ancient engineers even anticipated the chain gun