The Roman arsenal is able to make four units, "Bolt Shooter", "Siege Catapult", "Siege Catapult", and "Battering Ram". One of these Siege Catapults is unlocked from the "Marian Reforms" technology which states that it unlocked "Onagers", which are a type of catapult (https://en.wikipedia.org/wiki/Onager_(weapon)). A fix would be to rename the first Siege Catapult to "Onager", which was most likely supposed to be done before release anyway.