The Paris Métro or Métropolitain (French: Métro de Paris) is a rapid transit system in the Paris Metropolitan Area. A symbol of the city, it is noted for its density within the city limits and its uniform architecture, influenced by Art Nouveau. It is mostly underground and 214 kilometres (133 mi) long. It has 303 stations, of which 62 have transfers to another line. There are 16 lines, numbered 1 to 14 with two minor lines, 3bis and 7bis. Lines are identified on maps by number and colour, and direction of travel is indicated by the terminus.
It is the second-busiest metro in Europe, after Moscow. It carried 1.541 billion passengers in 2012, (up from 1.524 billion in 2011), 4.210 million passengers a day. It is one of the densest metro systems in the world, with 245 stations within the 86.9 km2 (34 sq mi) of the city of Paris. Châtelet – Les Halles, with 5 Métro lines and three RER commuter rail lines, is the world's largest metro (subway) station.
The first line opened without ceremony on 19 July 1900, during the World's Fair (Exposition Universelle). The system expanded quickly until the First World War and the core was complete by the 1920s. Extensions into suburbs and Line 11 were built in the 1930s. The network reached saturation after World War II, with new trains to allow higher traffic, but further improvements have been limited by the design of the network and in particular the short distances between stations. Besides the Métro, downtown Paris and its urban area are served by the RER developed from the 1960s, several tramway lines, Transilien suburban trains and two VAL lines, serving Charles De Gaulle and Orly airports. In the late 1990s, the automated line 14 was built to relieve RER line A.