The Great Northern Railway (Ireland) (GNR(I) or GNRI) was an Irish gauge (1,600 mm (5 ft 3 in)) railway company in Ireland. The Great Northern was formed in 1876 by a merger of the Irish North Western Railway (INW), Northern Railway of Ireland, and Ulster Railway. The Ulster Railway was the GNRI's oldest constituent, having opened between Belfast and Lisburn in 1839 and extended in stages to reach Clones in 1863. The Northern Railway of Ireland was itself formed by a merger of the Dublin and Drogheda Railway (D&D) with the Dublin and the Belfast Junction Railway (D&BJct).