Problem: In-game Ballista use arrows (or bolts), not bricks. It's definitely an antipersonnel weapon, not an ordinary siege (Though it's still a mechanism). So, it should be weaker than ordinary Catapult in terms of sieges and in the same time it shouldn't reduce the siege power of Roman Empire. The best way out of this situation is to change basic class of Ballista and allow it to share battlefield with Catapults and Trebushets.
UM - Ballista (Catapult Replacement):
available at Mathematics
100 Production Cost
8 CS, 14 RCS
"Legatus Legionis" (+1 Movement Point if GG is within 2 tiles)
2 Movement
no "Siege Inaccuracy"
no "Limited Visibility"
"Moves at Half-Speed in Enemy Territory"
Ballista (Composite Bowman replacement)
available at Engineering
120 Production Cost (+10 from CB)
9CS , 18 RCS (from 12CS,14RCS)
2 Movement
No Defensive terrain Bonuses
Cover I
"Legatus Legionis" (-15% CS to enemies within 2 tiles. +1 Movement Point if GG is within 2 tiles)
"Moves at Half-Speed in Enemy Territory"
Rationale: Roman army was not a part of bow’s Culture. There were almost no archers among them. The addition of "-15% CS to enemies" bonus will make Roman Legions even more powerful.
Spoiler Current Ballista :
UM - Ballista (Catapult Replacement):
available at Mathematics
100 Production Cost
8 CS, 14 RCS
"Legatus Legionis" (+1 Movement Point if GG is within 2 tiles)
2 Movement
no "Siege Inaccuracy"
no "Limited Visibility"
"Moves at Half-Speed in Enemy Territory"
available at Engineering
120 Production Cost (+10 from CB)
9CS , 18 RCS (from 12CS,14RCS)
2 Movement
No Defensive terrain Bonuses
Cover I
"Legatus Legionis" (-15% CS to enemies within 2 tiles. +1 Movement Point if GG is within 2 tiles)
"Moves at Half-Speed in Enemy Territory"
Rationale: Roman army was not a part of bow’s Culture. There were almost no archers among them. The addition of "-15% CS to enemies" bonus will make Roman Legions even more powerful.