How effective would artillery (as in scorpions, ballistae, etc) have been during the roman era in field battles? And how often were they used in that scenario?

by MrIDoK

I'm playing some Rome Total War and the artillery machines of that era always fascinate me, so i wanted to know a bit more about how good or bad they actually were.
And as a small extra, do you know of any books that talk about roman siege equipment, weapons and tactics?

elos_

You may be interested in this recent thread:

In ancient and medieval sieges, how were weapons such as catapults, ballistae, and trebuchets used? Were they used to break the walls, as in movies, or were they more used for wearing down the population in side by raining down destruction from above?

and

How would the Romans approach a siege?

May not answer what you're looking for directly but it's a start hopefully!