Good question. The video shows the first posts floating in air across the river and dropping magically in-place. These posts are then connected into a kind of s

Good question. The video shows the first posts floating in air across the river and dropping magically in-place. These posts are then connected into a kind of scaffolding for the caisson [1]. A pile driver is built on top of the scaffolding that is used to drive the remaining posts that make up the caisson wall but they don't show what powers the pile driver (men?) nor how it is moved post to post along the scaffolding. A water wheel is used to lift the water out of the caisson. The posts are small compared to modern piles so they will not be overly buoyant. Modern piles are core structural components that are used instead of a caisson so they are quite big. [1] https://en.wikipedia.org/wiki/Caisson_(engineering) https://en.wikipedia.org/wiki/Caisson_(engineering)