The line was created in 1926 as a means to join the rail stations the city had in the 1920s, and in preparation for the 1929 Universal Exposition. It has been growing since then to become, as of 2007, a large line made up of 30 stations, the network's busiest. These stations are architecturally homogenous, and as in the case of most metro lines in Barcelona, ornamentation is virtually absent from them. Some of them are improving their artificial lighting. Most of the line is underground, except for one short section, and at one point it shares tunnels with mainline tracks.