Onagers are the Tier 4 Siege units. They are weak against all troop types and for this reason should not be used to attack armies on resource tiles.
Onagers are the strongest possible unit against city defences i.e. wall traps. They also have the highest power and troop load of any unit. The downside is they are the most expensive troop to build in the game.
In order to unlock Onagers you must also max the entire combat research tree including siege defense and attack.
Onagers are over six times more expensive than their T3 counter parts Siege Towers , but do offer a significant increase in stats.
|1||9,600,000||9,600,000||7,200,000||15,360,000||9,600,000||288d||Academy 21, Siege Defense 10, Marksmen||Unlocks Onagers||768,000|