Why did they use caissons to build the Brooklyn bridge?

Caissons were used to build the piers for the Brooklyn Bridge because they provided a way to construct them underwater. Caissons are essentially large boxes that are sunk into the water and then filled with concrete or other material to create a solid foundation. Using caissons, the workers were able to create the bridge's piers in the middle of the East River without having to build temporary structures or divert the river's flow.