The Menai bridge was to have two main spans each with twin tubes (for double track), and the tubes were to be 406 feet in length. The central pier was to be 221 feet high. Work started at the site in July 1847 and by November 1848 fabrication of the main tubes was substantially completed. From 19 June 1849 the tubes for one line of track were floated into position and raised by jacks; the process was completed for the four main tubes by 7 January 1850. On 5 March 1850 Stephenson drove a test train through the completed single-track span of the bridge, and on 18 March 1850 public passenger trains started running. The Chester and Holyhead main line was connected throughout.