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In Greek antiquity, gravity, actuated by archers on city walls, turned many a tide, as victorious besiegers routed a city's land forces, but in the excitement of pursuit, got too close to the city walls! Xenophon presents one such instance as but the most recent of many cases, in relating the death of Teleutias.
The bow, among the Greeks, was the principal weapon for the city besieged. The bow being so effective in this situation explains why the an early advance in ancient siege machinery was the movable tower. It is an anti-gravity machine! Its purpose was to zero out the gravity advantage of arrows from heights! According to Vitruvius (10.13) Diades , Alexander's engineer, claimed the invention of the movable tower. You build it out of range, as high as the city walls, or even higher, armor the front with hides, move it up, and give your archers a fair chance to clear the city walls. Here, for once, is a situation where archers fighting archers is the main event in ancient Greece.