I really hate the common fiction image of a medieval army matching with siege engines. They were assembled on site, and you can’t really build a torsion spring on site. Ancient armies had significantly more organisation and labour (yay slavery) so they could bring the stuff with them.

tbf, the picture notes that the attackers would have constructed these on site.

Romans matched with dozens of onagers and scorpions, medieval armies mostly didn’t.

Fun fact - the Romans sometimes numbered prefabricated machinery parts so they could be assembled, disassembled, and repaired quicker.