The river, with its large tidal range (the Severn bore) and strong currents, made construction difficult. The pier columns were formed of cylindrical sections, about in diameter. Near the west bank, the bedrock was a long way below the shifting sands so much work had to prepare firm foundations. Staging was used through which the sections were lowered by chains, and when in place, filled with concrete. Near the east bank, a primitive piling machine was used to drive the sections through a ridge of clay. The staging was extended upwards for use while assembling the spans.