I recently took part in a siege defence as a defender against 2 besieging armies. 1 with catapults and 1 with ballistas. Of course seeing the ballistas I thought to myself... Well they can't exactly do anything with those but snipe my men on the walls, but Ooo, the catapults, those can breach my Huge Stone Wall (yes, highest upgrade). So upon start of game I send out some men on a "sucidal" mission to destory the enemy catapults, granted they did all die, but they killed the catapult operators and most of a armoured sergents unit. However to my surprize when suddenly I get the "your wall has been destoryed" frame.
My question about real ballistas is this... Since when can ballistas destory Huge Stone Walls? I obviously wasn't back in Medieval times but i'm pretty sure that at best, all they could do was catch a wooden wall on fire, and even then would be pressed hard to be lucky enough to do that.
I find it obsurdingly unrealistic for ballistas to be able to do that to stone walls. How come in Rome Total war the Ballistas couldn't do that? Why start now?

Now it´s a hole in the wall - still it´s a very spikey one. Better of without
the hole if you ask me.