Trebuchet are Renaissance artillery units. Like previous ages, they are still slow and not very useful at capuring/raiding map tiles. However, since the Renaissance Age offers no new infantry units, they have become more important. They have a faster, weaker variant called Couillards, and a slower, stronger variant called Firebrands. Barbarians tend to use a lot of their variant of this unit, Wallumbursts. They become obsolete in the Industrial Age.
Due to their slow speed, they are usually only useful at raiding close tiles. However if a player has the patience, these units can be sent in large numbers with other units into battles against strong barbarian forces.