Roman ballista

[D B Campbell]

Reenactment Gallery Photo: Ballista at Xanten event
Can anyone identify the group responsible for this splendid ballista? (Looks as if it's a forty-pounder.) I'd be interested to hear about the manufacturer's experiences.

[Praefectusclassis]

That piece belongs to the Römercohorte Opladen. We used to have some of their members around, but I'm not sure they still are.