Almost all selectable promotions in civ5 (meaning, the ones you select when a unit gains a level) have other promotions as requirements. The Civilopedia already lists the requirement for each promotion, but only its immediate ones; is there any chart or diagram summarizing this promotion prerequisite hierarchy?
Well I managed to produce one myself, though it took a few tries until I got the layout right. Click the image to see it full-sized. Explanation and notes below.