were advertised for the line in 1858 and the lowest offer of £81,637 by Richard Dunkley of Blisworth was accepted. The contractor had been an unsuccessful bidder for the contract to build Bridge Street station. Dunkley was also the successful tenderer for the line's stations, including Castle station at a cost of £612. It would be the most basic structure on the line with no goods facilities, limited passenger waiting accommodation and an awning over the single platform. Goods traffic was to be dealt with at Bridge Street. The station opened with the line on 16 February 1859. It was described in the L&NWR's minutes as a "very unassuming edifice", giving the impression that it was "merely temporary in nature" until traffic developed to a sufficient level to allow a "more imposing" structure to be built. 1880–81 rebuilding The advent of the Great Northern and London and North Western Joint Railway to tap the coalfields of Nottinghamshire and Yorkshire led the L&NWR to quadruple its main line between and Rugby and also to consider ways in which Northampton might be better served. In 1875, the L&NWR obtained powers to quadruple the main line north from Bletchley to , with the two new tracks (the "slow lines") diverging at Roade so as to form a new line (the "Northampton Loop") through Northampton. The result of these works would be to put Northampton on an important coal artery from Nottingham and the North to the L&NWR's Camden goods depot. Additional land would have to be purchased at Castle station to allow for expanded passenger facilities and goods facilities. Owing to the proximity of the River Nene, the only way this could be done was to expand onto the site of Northampton Castle. On 18 December 1876, the L&NWR purchased the site from William Walker and subsequently demolished the remains of the castle except for the postern gate which, following a local petition, was moved to a new site in the boundary wall of the new station where it remains to this day. £30,000 was allowed by the L&NWR board for the improvement of passenger facilities and a goods shed was constructed on the site of the castle in 1880. The rebuilt station opened with the Loop Line north to on 1 December 1881 followed by the line south to Roade on 3 April 1882. It comprised three through platforms and five terminal