Line 1 (Madrid Metro)

Line 1 of the Madrid Metro was opened on 17 September 1919 between Cuatro Caminos and Sol. It was extended from Sol to Atocha in 1921, Atocha to Puente de Vallecas in 1923, Cuatro Caminos to Tetuán in 1929, Tetuán to Plaza De Castilla in 1961 and Puente de Vallecas to Portazgo in 1962.

Between 1964 and 1966, station platforms were lengthened in order to allow 6-car train compositions, due to heavy increasing passenger flow. Chamberí station had to be closed because it didn't allow platform lengthening due to its sharp curve and its closeness to Iglesia station.

In recent years, the line has been extended both north and south. On 1 April 1994, it was extended from Portazgo to Miguel Hernández and on 4 March 1999 from Miguel Hernández to Congosto.

In 2007, the line was extended to Pinar de Chamartin in two stages. First, on 30 March 2007, the line was extended from Plaza de Castilla to Chamartin, which provides interchange with Line 10 and RENFE services. The new metro complex has line 1 and in the future, line 11 on the lower level and line 10 on the upper level. On 11 April 2007 the extension to Pinar daae Chamartin was completed. Here, there is interchange available to Line 4. There are two side platforms for arrivals and an island platform for departures. In May 2007, interchange to Metro Ligero 1 was available, which terminates one level higher.

On 16 May 2007, the line was extended south from Congosto to Valdecarros with two intermediate stations.

Since summer 2007 the line uses class 2000B stock. Chamberí station, after more than 40 years of abandonment, was refurbished and open in 2008 as an exhibition place to show how Metro stations were when opened in 1919.