The Metro 1 (Officially: Millennium Underground Railway or M1) is the oldest line of the Budapest Metro system. Known in Budapest simply as "the underground" ("a földalatti"), it is the second oldest underground railway in the World (the first being the London Underground's Metropolitan Line), and the first on the European mainland. It was built from 1894 to 1896. In 2002, it was listed as a UNESCO World Heritage Site.
M1, the oldest of the metro lines operating in Budapest, has been in constant operation since 1896. The original purpose of the first metro line was to facilitate transport to the Budapest City Park along the elegant Andrássy Avenue without building surface transport affecting the streetscape. The National Assembly accepted the metro plan in 1870 and German firm Siemens & Halske AG was commissioned for the construction, starting in 1894. It took 2000 workers using up-to-date machinery less than two years to complete. This section was built entirely from the surface (with the cut-and-cover method). Completed by the deadline, it was inaugurated on May 2, 1896, the year of the millennium (the thousandth anniversary of the arrival of the Magyars), by emperor Franz Joseph. One of these original cars is preserved at the Seashore Trolley Museum.
The line ran underneath Andrássy Avenue, from Vörösmarty Square (the centre) to City Park, in a northeast-southwest direction. The original terminus was the Zoo (with extension to Mexikói út in 1973). It had eleven stations, nine underground and two overground. The length of the line was 3.7 km at that time; trains ran every two minutes. It was able to carry as Many as 35,000 people a day (today 103,000 people travel on it on a workday).