The Engineer is an Epic Battles role which focuses on utilizing interactives and siege equipment within the space to defeat their enemy.
The majority of their promotions focus on improving the efficiency with which they perform their actions and unlocking new options for utilizing and upgrading siege weaponry.
Engineers also gain the ability to place a variety of traps that can damage or hinder opponents.
Large army warfare requires siege weaponry. The Rohirrim are armed with various sizes of catapults and ballistae positioned throughout the fortress of Helm's Deep. Taking command of these weapons, you can choose ammo with which to load them, aim them, crank them, upgrade them, and fire them. If you have an ally with you, they can aid you in any of those actions, or do one of their own. The actions you have available, and the efficiency with which you perform them, can be unlocked and upgraded through the Promotions tab of the Battle for Helm's Deep panel.
While all characters can operate siege equipment, only the traits available to an Engineer increase their efficiency and potency.