The use of steel in the bridge's construction was perhaps the most significant innovation mandated by John Roebling. Before this time, large-scale steel structures had been built using iron as the primary material, but this method was expensive and difficult to execute on a scale commensurate with the demands of a major bridge. The use of concrete as a binding agent for the steel was also an innovation proposed by John Roebling that was eventually adopted by most other bridge designers. John Roebling's involvement with the design process resulted in several important innovations being used in the construction of the Brooklyn Bridge. First, he proposed using wire rope instead of chains as the main form of suspension between the two towers. This would later be adopted by many other designers when building their own bridges. Second, he suggested that the deck of the bridge be made of precast segments bolted together in the shape of cross ties (the horizontal members of a truss) to reduce the weight of the structure and make it more flexible. This idea was also soon adopted by others. Finally, Roebling proposed that the foundation of the bridge should be built of stone instead of dirt. This requirement was probably intended to provide better drainage and avoid problems with soil instability resulting from changes in water level as the river flows through its course.