The Brussels metro dates back to 1976, but underground lines known as the "premetro" have been serviced by tramways since 1968. It is the only rapid transit system in Belgium (Antwerp and Charleroi both having light rail systems). The network consists of four conventional metro lines and three "premetro" lines. The metro-grade lines are M1, M2, M5, and M6, with some shared sections, covering a total of . , the metro network within the region has a total of 69 metro and "premetro" stations. The metro is an important means of transport, connecting with six railway stations of the National Railway Company of Belgium (NMBS/SNCB), and many tram and bus stops operated by STIB/MIVB, and with Flemish De Lijn and Walloon TEC bus stops.