A Ballista is a powerful crossbow that is fixed to the ground, or is placed on a moving platform.
It fires huge wooden bolts, sometimes even coated in a flammable mixture and lit. Its often used to shoot down things such as enemy ships or city walls. The weapon was first used by Alexander the Great in his conquest of Persia to batter away at the walls of a city.
A smaller version, called the Scorpion was invented by Archimedes of Syracuse in the 3rd Century BC during the Punic Wars. The Romans later adapted the ballista and used it for both sieges and massive field battles. After the Fall of Rome, the ballista disappeared from the West, yet the Byzantines used it extensively in their battles. This was brought back to Western Europe during the Crusades, although it was mainly used for besieging castles by that time. The arrival of gunpowder deemed the Ballista as outdated and impractical for siege warfare by the 15th Century.
In the God of War Series
God of War: Ascension
Ballistas can be found in two Multiplayer maps: The Walls of Troy and the Bog of the Forgotten. They are usually placed next to an altar to prevent enemy players from capturing them. When using a ballista, a player must press Square, Triangle, Circle or X in order to decide where to fire the arrow. Before the arrow hits the target, its fire will illuminate the ground, warning players about the hazard. These arrows deal a great damage when they hit players.
God of War: Chains of Olympus
At the beginning of the game, during the Siege of Attica by the Persians, Eurybiades, leader of the Attican army, tries to reach a ballista in front of him to return fire against the Persians, but dies before it due to his wounds. Kratos then uses this ballista to fire back at the enemy and hits one of their ships, sinking it. After this, the Persians fire once again, hitting and destroying this ballista with an arrow and opening a passage on the floor with another.
Later in Attica, after defeating the Persian King, another one can be found. The Basilisk can be seen on the background, spitting fire and destroying the city. After defeating the enemies, Kratos uses this ballista to fire at the beast, hitting its neck. It then screams at Kratos, angered, and goes away. By spinning this ballista and firing it against a building, the arrow will destroy its wall. This building is reached moments later and contains a hidden chest. If the wall is destroyed before leaving the ballista area, it's possible to reach this chest.
God of War
In the Fortress of Athens, two ballistas can be found. The first one is very big, and its arrows are so powerful that can destroy wood doors, some stone walls and kill Minotaurs instantly. It can be spinned by pulling a lever behind it. Hidden chests can be found at each side of it and can be reached by destroying the walls in front of them and then by finding a way to get to them.
A smaller ballista can also be found later in the Fortress. Its arrow pulls a rope that Kratos must climb on in order to reach the other side of a gap.
Another one is found in the Rooftops of the city and can be moved. Kratos must move and rotate it on a platform to make it face the right direction, and then use it to fire against a door, destroying it and revealing the path to Zeus' Fury.
In the Challenge of Hades in Pandora's Temple, another huge ballista points to a big and massive wood door with an iron lock. The arrows fired by this ones are also huge and fiery, but are not powerful enough to destroy the door. When Pandora's Guardian comes out of this door, the ballista is essential to beat the beast. Kratos must fire it against the giant bull in order to destroy parts of its armor and then, when it's completely destroyed, to kill the Guardian: the final arrow hits the bull's chest, stabbing it against the wood door behind it. Not even this blow destroyed the door, but before dying, one of the Guardian's feet hits the base of the door, opening a whole that is big enough for Kratos to get through.
God of War II
At the beginning of the game, during the first fight against the Colossus of Rhodes, a big ballista can be found at the far left of the battlefield, with a huge stone ready to be fired at the Colossus' head. If the stone is fired against him when he's still fighting, he will simply grab it and smash it with his huge hands. If it's fired when he's stunned, it will hit his head, granting Kratos orbs. After firing the stone, Kratos must fire himself against the Colossus while he's still stunned, which will initiate a quick time event to blind his eye.
God of War III
In Olympia, Kratos finds Helios battling the titan Perses on his chariot. In order to take down the god, Kratos must use a ballista on one of the buildings. When it hits Helios, he gets disoriented and Perses uses this opportunity to grab his chariot, smash it in his hand, causing a light explosion, and throw it away against the mountain. He then continues to climb Olympus, while Kratos goes after the injured sun god.
The Chamber of Daedalus has a very similar ballista which can be spinned to left of right. The arrow it fires pulls a rope, and when this arrow reaches a wall, Kratos can climb on the rope to reach this point. The Chamber has also many magic portals, each one leading to a different part of it. By firing the ballista at these portals and then climbing on the rope, it is possible to reach many hidden chests, including the one that contains Daedalus' Schematics, one of the game's godly possessions. By pulling a crank located at the right side of the Chamber, the floor beneath the ballista will be leveled up, allowing Kratos to fire it at different points and portals and thus reach different hidden chests.