Line 1 is the oldest line of the Budapest Metro, it was built from 1894 to 1896. It is known locally as "the small underground", while the M2, M3 and M4 are called "metró". It was the first underground on the European mainland, and the world's third oldest underground after the London Underground and The Glasgow Subway.

The Budapest Metro is the rapid transit system in the Hungarian capital Budapest. Opened in 1896, it is the world's second oldest electrified underground railway after the City and South London Railway of 1890, now a part of London Underground, and the third oldest underground railway with multiple stations, after the originally steam-powered Metropolitan Railway, now a part of London Underground (1863), and the Mersey Railway, now part of Merseyrail in Liverpool (1886).