Many Greek engineers were hired to build siege engines or teach the subjects of Rome.  This machine does not have a frame, which can allow the half-springs to be disassembled for easy transport on wagons, probably because it is far smaller than the average ballista, and can be transported with the springs still attached to the main part of the engine (the ladder/table assembly). 

This type of engine was more powerful that the euthytone type catapulta, which was usually used only for launching javelins (large arrows).  Engineers from Rhodes were known to modify the powerful palintones to shoot javelins as well as round stone shot, making their machines much more versatile.