The * indicates that the civilization can fully upgrade their Catapults, i.e. gets Alchemy, Engineering, and Ballistics.
The ^ indicates that the civilization has at least one civilization bonus that benefits the combat strength of their Catapults.
The direct upgrade of the Stone Thrower, they are fairly expensive and more effective, but less so than the Heavy Catapult. They also have a minimum range of 3. Catapults deal 28 bonus damage against buildings (to a total of 40 damage, since buildings in Age of Empires have 80% resistance to all attacks) but only 10 bonus damage against towers (to a total of 22 damage).