The steel lattice girder Koilwar Bridge (known as Sone Bridge when it was built) was the longest bridge in the subcontinent when built: construction started in 1856, disrupted by the Revolt of 1857, and completed in 1862. A two-lane road (Old NH 30) runs under the twin rail tracks. It connects Arrah on the west side to Bihta, Danapur and Patna on the east side of Sone river.