Catapults store energy using elastic deformation, like a bow; counterweight trebuchets store energy using gravity.
replyDidn't the Romans have something similar?
replyThe Romans had onagers and ballista, both of which work via string tension. Then around 6AD it seems string traction (mangonels) where introduced from China and finally counterweight/gravity was introduced in the 12th century.
replyBasically more primitive versions of the same.
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