The Valtellina is situated in the north of Lombardy, on the border between Italy and the Swiss canton of Grigioni, and it is the only major Alpine river valley running from east to west. It is 120 kilometres long and about 65 wide. It has two main wide valleys: that of the Adda, which rises near Bormio, passes through upper and lower Valtellina and empties into Lake Como; and that of the rivers Lira and Mera, which corresponds to the Valchiavenna region from the Spluga Pass and from Val Bregaglia to Lake Mezzola. The peaks of the Valtellina are more than four thousand metres high with the Pizzo Bernina, and those associated with Ortles, Cevedale, Gran Zebrù and the Adamello Presanella group. The Rhaetian Alps to the north include some broad valleys, including those of the Valmalenco and Valmasino, in addition to the large basins of Bormio and Livigno. On the southern side, the Bergamo Alps form narrow and wild valleys. The east-west arrangement makes the Valtellina particularly suitable for viticulture. On the Retico slopes, sunlit and protected from the winds, 2,500 kilometres of dry stone walls have been constructed over the centuries. It was an enormous task which supports the terraced vineyards from which the Valtellina wines are produced. The Stelvio Pass at 2,758 metres is the highest in Italy and the second highest in Europe. It leads over to the South Tyrol and is also linked with legendary stories of the Giro d'Italia. At 2,621 metres, the Gavia Pass, the link with the Valcamonica, is slightly lower.