The Ballista yard is a building from the Stronghold town in Heroes of Might and Magic III. A structure unique to the Stronghold, it is an upgrade of the Blacksmith that offers ballistae (the regular Stronghold Blacksmith produces ammo carts). The Ballistae are sold at normal prices (2,500 gold), and thus the only war machine a hero cannot purchase in a Stronghold is the first aid tent. This is not a large loss, because the native Stronghold heroes are not proficient with first aid, but the tent is still useful for unboosted healing.
The Ballista Yard has the Blacksmith as a prerequisite, but is not required for building other structures. It costs 1000 gold and 5 wood.