@AkashaX1885 It is an intenional design that horses can not enter cities. Acctually it is not that they can not enter cities, but rather thant they can not climb city walls. It was highly requested by people in the forums already after the first OpenDev. In the firts OpenDev horse units could "climb" the walls and attack inside the city. That is why siege weapons of some sort is very much recommended to breach the walls first, or at least bring some non mounted melee units with You to a siege. If it is the AI who make the sieghe and do not make siege weapons, or You attempt to attack out from the city before they do, I can see how this can cause a situation like You describe. Maybe something they need to look into for sure if it becomes like a prolonged period of turns where nothing happens, or a huge delay if haven chosen auto resolve combat.