The engineers Carlos Mendoza, Miguel Otamendi and Antonio González Echarte developed a suburban
railway project for the city of Madrid.
On the 17th of October of 1919, the King Alfonso XIII officially inaugurated the first line between Puerta del Sol, and Cuatro Caminos, with a total longitude of 3.48 Km, and 8 stations. It took 10 minutes to complete the route, which meant a considerable time reduction compared to other means of transportation. On the 31st of the same month, the Metro was opened to the public service.