The Koilwar Bridge (known as Sone Bridge when it was built) is amongst the older of the longer bridges in this subcontinent. Although construction started in 1856, it was disrupted by uprisings in 1857 and completed in 1862. It was inaugurated by the Viceroy Lord Elgin, who said, “... this magnificent bridge was exceeded in magnitude by only one bridge in the world”. The 4,726 feet (1,440 m) bridge was designed by James Meadows Rendell and Sir Matthew Digby Wyatt. It remained the longest bridge in the Indian subcontinent till was overtaken by the Upper Sone Bridge in 1900.
The steel rail-road bridge is shown in the film Gandhi. A two lane road (NH 30) runs just under the double rail tracks. Sand mining near the pillars of this old bridge has created structural problems recently.
An initial survey of the bridge site was made on 17 February 1851 by George Turnbull, Chief Engineer of the East Indian Railway Company: he determined that the river then was 5350 feet across—the completed bridge in 1862 was 5280 feet across. He settled on the site near Pures "where the banks are well defined, and the channel had evidently for ages been confined within certain limits, proved by the existence of old Hindoo temples, far before the Mohammaden works at Muneer, built about 200 years [before 1851]."
By November 1859, both abutments and 16 of the 26 piers were being built and the well-sinking for the remaining piers progressing. By 21 December 1860, three of the iron spans were in place; 4572 tons of the estimated 5683 final tons of iron-work for the bridge had arrived from England.
George Turnbull inspected the bridge and judged it complete on 4 November 1862. On 11, 12 and 13 December 1862, "a set of experiments with couple engines, testing the Keeul, Hullohur and Soane bridges, with an assembly of Government engineers, and our railing engineers; all very satisfactory." On 5 February 1863, a special train from Howrah took Turnbull, the ViceroyLord Elgin, Lt Governor Sir Cecil Beadon and others over two days to Benares: they alighted at the bridge and inspected it. In Benares there was a durbar on 7 February to celebrate the building of the railway and particularly the bridging of the Sone, the largest tributary of the Ganges.