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The STIB/MIVB was created in 1954. The first underground tramway (or premetro) line was built between 1965 and 1969; it ran from Schuman to De Brouckère. In 1970 a second line was opened, between Madou and Porte de Namur/Naamsepoort.

An underground station at Diamant was opened in 1972 and the "outer ring" line was extended from Diamant to Boileau station in 1975. Since then, this underground tramway section has not been developed further. It is currently used by tramway lines 23, 24 and 25.

Rogier station was inaugurated in 1974.

It was only on September 20, 1976 that the first metro was brought into service. One branch went from De Brouckère to Beaulieu (in Auderghem), and the other one linked De Brouckère with Tomberg (in Woluwe-Saint-Lambert). The same year, the North-South Axis (premetro) was opened between the North Station and Lemonnier. In 1977 two new stations were built: Sainte-Catherine/Sint-Katelijne which replaced De Brouckère as the last stop in the municipality of Brussels, and Demey which replaced Beaulieu as the last stop of the southern branch.

The next step in the extension of the metro was the opening of three metro stations in Molenbeek-Saint-Jean (namely Beekkant, the new end of the metro line, Etangs Noirs/Zwarte Vijvers and Comte de Flandre/Graaf van Vlaanderen).

In 1982, line 1 was split into two different lines: line 1A going from Bockstael (in Laeken, a former municipality now merged with Brussels) to Demey (Auderghem) and the line 1B going from Saint-Guidon/Sint-Guido (in Anderlecht) to Alma (in Woluwe-Saint-Lambert).

Three years later, line 1A was extended to Heysel (near the site of the 1958 World Fair and the Heysel Stadium) at one end and to Herrmann-Debroux at the other end. That year was also the one which saw the opening of the station Veeweyde on line 1B, as well as that of Louise/Louiza on the premetro line dug under the small ring (from Louise/Louiza to Rogier).

This line was extended to Simonis the next year and was finally opened as an official metro line in 1988, known as line 2, then going from Simonis to the South Station. The stations of Kraainem/Crainhem and Stockel/Stokkel were also inaugurated in 1988 on the line 1B. At the other end of this line, Bizet station opened in 1992. It was then the turn of line 2 to reach Clemenceau in 1993. The premetro section known as the North-South Axis, sometimes referred to as line 3, was also extended to Albert that year with 5 new premetro stations (South Station, Porte de Hal/Hallepoort, Parvis de Saint-Gilles/Sint-Gillis Voorplein, Horta and Albert).