The Helepolis fires faster than the Ballista and has +1 range. It is strong in groups as it is fairly accurate and deals the highest damage per second in the game. Like its predecessor, the Helepolis does not deal bonus damage against buildings but deals a +5 attack bonus against Fire Galleys.
The main counter to the Helepolis are Catapults that can out-range and eliminate them in a single shot, unless the unit moves clear of the attack. No civilizations have bonuses for this unit.
Due to the fast fire rate at a long range, the unit may still fire a bolt or two within a fraction of a second even after the enemy unit is eliminated.
Typing ICBM allows the player to upgrade its range by 90, bumping the total up to 100 range.
Although the firing range will be improved, the line of sight still remains the same. Likewise, it cannot attack any target unless the unit is already discovered within the fog of war. Even if the fog of war is removed by a cheat code, it still cannot attack moving targets unless it is within the line of sight of other allied units. However, it may attack enemy buildings already discovered through the fog of war.
Typing this code before finishing researching Engineering will grant the player an additional 2 range. This will affect both the firing range and the line of sight.
The name is a misnomer. Helepolis was actually a name for Greek siege towers, not a siege weapon firing bolts or rocks.
The helepolis (Greek for "city killer") was one of the most advanced weapons of antiquity and a remarkable demonstration of ancient engineering ingenuity. It was in fact an automatic siege weapon that fired ballista bolts. The top loading lagazine of the helepolis was a horizontal funnel in which were laid bundles of bolts. These were fed by gravity into the chamber of the weapon. A clever gearing mechanism automatically recocked the helepolis and fired. Human operators needed only to keep it loaded and aimed, plus providing power by cranking. The original of the machine was abandoned outside the city of Rhodes when a besieging army withdrew. It has been reconstructed on paper from contemporary sketches and descriptions of that only known example.
—Age of Empires manual
A group of Helepolises
Ballista (above) and Helepolis (below) range compared. Take note that the helepolis has fired two projectiles at a given time fraction.