How effective was Roman artillery in Field battle?

[Mrbsct]

How effective were weapons like the Scorpio and Ballista in a field battle? Were they ever used decisivly in a field battle?

[Marja]

Do river crossings count? I recall some mention of Drusus using artillery to support river crossings.

[Jori]

They were worth the sacrifice of two legionaries of Antonius Primus, that courageously broke Vitellius's artillery, but lost their lives after that.

Antonius Primus won the battle of Bedriacum, that led ultimately Vespasian to be emperor.

[Valerian Pertinax]

Most of what I've read seems to cast ranged weapons as a supporting means of winning a battle, but not what one would depend on to get the job done. Even in battles where projectile weapons played a starring role (Agincourt and Carrhae come to mind), there was still a significant hand-to-hand element.
In all of the diagrams of a paper- strength legion I've ever seen, ballista and scorpions seem to be frequently missing. I can't readily recall many instances where they were even mentioned during a field battle, let alone "decisive", but this may just be that their presence was either taken for granted, or not of as much use as the first ten minutes of Gladiator would have us believe
What reference to Roman ballista I do recall have more to do with sieges. Caesar used scorpions to defend his fortifications during the siege of Alesia ,where I imagine they came in pretty handy mounted on top of a tower. During the siege of Jerusalem, ballista were used to keep defenders off the walls, a huge help to the legionaries trying to take a fortified position. Ditto for Maiden castle In Britain.

[P. Clodius Secundus]

Roman military tactics seem to have favored offensive operations, at least more so than the Greeks who raised
siege warfare and it's technolgy almost to an art. Despite the fact that ballistae and even the early scorpions
were not ideally suited for mobile field warfare, the Romans adopted and used them widely enough that they seem
to have taken them nearly everywhere. Many of their developments seem to have focused on making the lighter weapons
more useful in open-field warfare. As case can be made that with the development of the iron-framed arrow shooting
ballista and further modification of an itallic Ashaped base developed in the early Pricipate they were able
to arrive at the first true field-artillery piece, the carroballista.

[M. Demetrius]

can't readily recall many instances where they were even mentioned during a field battle, let alone "decisive", but this may just be that their presence was either taken for granted, or not of as much use as the first ten minutes of Gladiator would have us believe

Or maybe they didn't use them in places where they lacked giant amphorae of flaming oil and spherical hay bales?

[Flavivs Aetivs]

The Romerschiffe finds had mounts for a Scorpion on the larger patrol vessel, so they were probably common on river patrol boats and liburnae. We know Ammianus mentions they could fire across the danube, which was proven with the "firefly" device over in (Hungary?) So they would have been useful in things like river crossings. Also made for a good scare tactic.

Later on there were supposedly crossbow-versions of them used in the late roman army, but there is limited evidence of that.

[Valerian Pertinax]

can't readily recall many instances where they were even mentioned during a field battle, let alone "decisive", but this may just be that their presence was either taken for granted, or not of as much use as the first ten minutes of Gladiator would have us believe

Or maybe they didn't use them in places where they lacked giant amphorae of flaming oil and spherical hay bales?

Even if you don't have the giant flamey hay bales or exploding ballista bolts, I see no excuse to not at least light your pila on fire before throwing them.