The polybolos was an advanced ancient Greek repeating ballista, often described as a "machine gun of antiquity," invented in the 3rd century BC by Dionysius of Alexandria. It used a unique chain-drive and gravity-fed system to fire bolts in rapid succession
I've heard of this, but what's the advantage? They still need to recharge the torsion the same way, which must've taken longer than someone manually feeding the next bolt.
Apparently it was on MythBusters, but I don't remember that one.