The Roman army had portable ballista. I would say it would take about a minute to set-up, and two move actions by two different people to cock. Firing is a standard action by an individual. Proficiency bonus +3. I would tend to go high in damage considering the inflation of hit points in 4E. 5d10 per hit, can get two targets if they are inline. Range 40/80.
I found this from a web site, I think it would take many minutes to set up?
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The ballista is a siege weapon, invented by the
ancient Greeks, and quickly adopted by the
roman army. The ballista resembles a large
crossbow, mounted upon a large-based monopod stand, allowing the weapon to be aimed without needing to be picked up. The Roman version was intended as an infantry support weapon, the various versions having a span of four to eight
feet across, enabling it to be carried around by its operators, and used in rough terrain. The
ballista was the largest siege weapon to see regular use in the roman invasion of
Britain
Unlike a crossbow, the tension in a ballista is stored not it the arms, which are wide and rigid, but in large bundles of
rope or
sinew at the front of the machine. It was
drawn using a system of levers that pulled a trolley (that held the bolt holder) back over a ratchet, and a
trigger that detatched the bolt holder from the trolley. The ballista fires a five foot wooden
bolt, with a steel tip, capable of penetrating almost anything the army would have to face on the
battlefield. The ballista could even be used in a
seige, firing bolts through the walls and roofs of
hill forts.
Skeletons of ballista
casualties have been found, with ballista tips embedded between
vertebrae, and square holes in their
skull where a ballista bolt had gone straight through.
Modern
replicas of the ballista have been created using the same materials and techniques available to the
Romans, and skilled operators have shown the machine to be capable of firing three or more bolts per minute, over a range of five hundred meters or more. The Romans also used a repeating ballista, which automatically
loaded and
fired the weapon, the operators only having to turn the handle. Replicas of this
repeating ballista can fire twelve or so shots per minute.