It crosses Rome diagonally from north-east, starting at Rebibbia and at Jonio stations, to south, terminating at Laurentina, in the EUR district.

The line was planned during the 1930s by the Fascist government in search of a rapid connection between the main train station, Termini, and a new district to the south-east of the city, E42, the planned location of the Universal Exposition (or Expo), which was to be held in Rome in 1942.

When work was interrupted some of the tunnels on the city-centre side of the metro (between Termini and Piramide) had been completed and were used as air raid shelters during the war.

Work on the metro began again in 1948, in concert with turning the space, formerly designated for the Expo, into a commercial district under the name Esposizione Universale Roma (EUR).

The line was officially opened on 9 February 1955 by the President of the Republic Luigi Einaudi.