Ballista

These large siege weapons resemble giant crossbows and are permanent fixures of a map &mdash; they cannot be "picked up", moved, or even aimed. They can still be used, however, by enemies and players alike. Each ballista has a lever near it, simply click on the lever and the weapon will fire at its preset range and direction, causing a very powerful explosion where it hits. It does not need reloading, but it does take a couple seconds before it can be fired again.

Ballistae are primarily found in the Shiverpeak Mountains, at areas of strategic importance. Most Ballistae break when you kill the NPC controller.

External Links

Wiki Ballista