Working in parallel to the onsite construction process, the two central tube sections, which weighed apiece, were separately built on the nearby Caernarfon shoreline. Once they had been fully assembled, each of the central tubes was floated, one at a time, into the causeway and directly below the structure. The in-place sections were gradually raised into place using powerful hydraulic cylinders; they were only raised by a few inches at a time, after which supports would be built underneath the section to keep it in place. This aspect of the bridge's construction was novel at the time. Reportedly, the innovative process had been responsible for costing Stephenson several nights of sleep at one stage of the project. The work did not go smoothly; at one point, one of the tube allegedly came close to being swept out to sea before being recaptured and finally pushed back into place. The tubes were manoeuvred into place between June 1849 and February 1850.