|“||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 and projectile speed, minimum range, high cost, and tendency to harm friendly units caught in its blast.
Siege Onagers can attack the ground and cut down trees, making them very useful in cutting a quick path to somewhere.
The * indicates that the civilization can fully upgrade their Siege Onagers, i.e. gets Siege Engineers. Faith and Heresy are not taken into account because they only contribute to their combat strength in a very situational manner.
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, they excel at crushing other siege weapons, 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 do not 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 Bulgarians, Celts, Ethiopians, Koreans, Teutons and Slavs as all have either a civilization bonus or unique technology that benefit the strength of both.
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. Compared to the Onager, the Siege Onager has more health, damage, and pierce armor, but perhaps more importantly has a larger blast radius, making shots harder to dodge and able to hit more targets.
Upgrading to Siege Onager helps even 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 needs two attacks from a Bombard Cannon to be taken down, 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.
|Unit strengths and weaknesses|
|Strong vs.||Buildings, Villagers, archers, Scorpions, Battering Rams, Trebuchets, units in dense formations|
|Weak vs.||Melee units especially Magyar Huszars and other melee cavalry, Mangudai, Woad Raiders, Condottieri, Bombard Cannons, Eagle Warriors|
|Hit points||Furor Celtica ( , Celts only)|
|Attack|| Siege Engineers (+20% attack against buildings)|
Torsion Engines (increases blast damage radius, Ethiopians only)
Counterweights (+15% attack, Saracens only)
|Range|| Siege Engineers (+1)|
Shinkichon ( , Koreans only)
|Armor||Ironclad (+4/+0, Teutons only)|
|Movement Speed||Drill (+50%, Mongols only)|
|Conversion defense|| Faith|
First Crusade (Sicilians only)
- Aztecs: Siege Onagers are created 11% faster.
- Bulgarians: Upgrading to Siege Onager costs -50% food.
- Celts: Siege Onagers fire 25% faster. Siege Onagers can convert herdables even if enemy units are next to them.
- Slavs: Siege Onagers are 15% cheaper.
- 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.
- A team containing Lithuanians: Researching Heresy and Faith is 20% faster.
The Age of Kings
- Onagers move at a speed of 0.5.
- Researching Chemistry reduces the projectile speed from 3.5 to 2.9.
- Siege Onagers 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 1.0b, the effect was reduced to +1.
- A team containing Koreans: Siege Onagers have +1 range.
- Researching Chemistry does not affect the projectile speed anymore.
- Celts: Furor Celtica gives +40% HP to Siege Onagers.
- Teutons: Ironclad introduced.
- A team containing Koreans: Siege Onagers minimum range reduced by 2 (instead of +1 range).
Lords of the West
- Sicilians: Initially, cannot train Siege Onager. With update 47820, they get access to the Siege Onager.
Dynasties of India
- With update 61321, siege units and ships are now resistant to armor-ignoring attacks, similarly to buildings.
- Saracens: Counterweights introduced.
- 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. With the release of the Definitive Edition, however, the Siege Onager is tied with the Paladin as the most exclusive unit in the game. With update 36906, that title was won again by the Paladin. With Burgundians introduced, it is now tied again. With the Sicilians gaining access to the Siege Onager in update 47820, the Paladin has won the title again.
- Coincidentally, the four civilizations that have access to the Siege Onager in The Age of Kings are playable in the campaigns.
- None of the civilizations in Rise of the Rajas or Dawn of the Dukes have access to it. The former result in the condition that none of the Southeast Asian civilizations have access to Siege Onager. At the release of Lords of the West, none of the two civilizations in Lords of the West had access to the Siege Onager either; However, the Sicilians have access to the Siege Onager since update 47820.
- Both African civilizations have access to Siege Onager.
|“||The siege onager was the largest upgrade of the onager line of weapons. It had the longest range and did the most damage.||”|
|—Age of Empires II manual|
In the Ancient Roman Empire, Onagers were designed to be used against lightly fortified towns, and massive armies, and thus the upgrade of this, armed the Onager with metal plates, were built 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.