Siege Onager

"Stronger than Onager. Wheeled siege weapon used to attack a small mass of units."

- Age of Empires II description

The Siege Onager is a ranged siege unit in Age of Empires II that can be trained at the Siege Workshop once the Imperial Age is reached. It is primarily used against large groups of enemies. Its high attack and splash damage make it a powerful unit, especially against archers and slow-moving units. Its main offsets are its low movement speed and projectile speed, minimum range, and tendency to harm friendly units caught in its blast. Siege Onagers can attack ground and cut down trees.

Tactics
Siege Onagers are arguably the most powerful siege weapon when it comes to killing other units. They are devastating against archers and slow-moving units, but cannot defend themselves against most melee units. Therefore, they need to be guarded in most situations. Archers are often used, because own melee units are usually endangered by the own Siege Onagers. But archers don't cover the Siege Onager's main weakness adequately, which is cavalry. Therefore, Siege Onagers are also often paired with Halberdiers. That combination is especially prominent with the Celts, Ethiopians, Koreans, and Slavs.

As Siege Onager is one of the most expensive upgrades in the game (but also one of the most powerful), the player has to carefully weigh whether it is worth it in a 1v1 game, but it can definitely turn the tide of a game with a few good shots in the right situation.

Upgrading to Siege Onager helps evening out the playing field against one of the Mangonel-line's main weakness, the Bombard Cannon, to some extent. The reason for this is that the Siege Onager can take two Bombard Cannonballs, but can kill a Bombard Cannon in one full shot, while for the standard Onager it is the other way around. The large drawback of the much shorter range compared to the Bombard Cannon still remains however, so considering equal micromanagement skills and numbers, the Bombard Cannons should still come out on top. Another point to consider is invested resources: While the initial Siege Onager upgrade is very expensive, Bombard Cannons only require Chemistry (which is also useful for other ranged units), but Siege Onagers themselves are cheaper than Bombard Cannons, so in small numbers the Bombard Cannon is cheaper, but the higher the production numbers go, the more it evens out, until the cost of the Bombard Cannons actually surpasses the cost of Siege Onagers.

Siege Onagers are very effective against naval units. The AI will also use Siege Onagers as a shore defense to protect its buildings.

Siege Onagers are able to cut down trees, making them valuable in maps with large areas of forests like Black Forest by enabling to the player to attack from behind a forest.

Civilization Bonuses

 * Aztecs: Siege Onagers are created 15% faster.
 * Celts: Siege Onagers fire 20% faster. Siege Onagers can convert herdables even if enemy units are next to them.
 * Slavs: Siege Onagers are 15% cheaper.

Team Bonuses

 * A team containing Celts: Siege Onagers are created 20% faster.
 * A team containing Koreans: Siege Onagers.
 * A team containing Malians: Researching Chemistry and Siege Engineers is 80% faster.
 * A team containing Teutons: Siege Onagers are more resistant to conversion.

The Age of Kings

 * Onagers move at a speed of 0.5.

The Conquerors

 * Siege Onagers now move at a speed of 0.6.
 * Siege Onagers gain +12 bonus damage against siege weapons.
 * Heresy introduced.
 * Celts: Furor Celtica introduced. It gives Siege Onagers +50% HP.
 * Mongols: Drill introduced.
 * Koreans: Shinkichon initially gives Siege Onagers +2 range. With patch 1.0c, the effect was reduced to +1.
 * A team containing Koreans: Siege Onagers have +1 range.

The Forgotten

 * Celts: Furor Celtica now gives +40% HP to Siege Onagers.
 * Teutons: Ironclad introduced.
 * A team containing Koreans: Siege Onagers minimum range reduced (instead of +1 range).

Trivia

 * The total cost to upgrade Mangonels to Siege Onagers is 2,250 food and 1,500 gold, making Mangonels the most expensive units to upgrade.
 * Despite the description given in the manual for the Siege Onager, it does not have any additional range over the Onager.
 * Before The African Kingdoms was released, the Siege Onager was the most exclusive unit in the game, i.e. no other unit was available to fewer different civilizations. With the introduction of The African Kingdoms, however, that title was lost to the Paladin. The Siege Onager remains the second most exclusive unit with only nine civilizations being able to train them.
 * Of all the civilizations having access to Siege Onagers, the Malians are the only one not having access to Siege Engineers.
 * Before The Forgotten, researching Chemistry had a negative effect on the Siege Onager's projectile speed, lowering it from 3.5 to 2.9.

History
''The siege onager was the largest upgrade of the onager line of weapons. It had the longest range and did the most damage.''

In the Ancient Roman Empire, Onagers were designed to be used against lightly fortified towns, and massive armies, and upgrade of this, armed the Onager with metal plates, were twice the size and could fire medium and even large boulders to weaken walls that rams were not able to access. However, the Byzantines do not have access to the Siege Onager, despite being the Roman Empire's continuation.

In Medieval Times, Mangonels and Trebuchets were used in sieges as they proved to be more useful against large fortified walls.