Ticino has a long tradition of winemaking, being the southernmost region of Switzerland. Wine has been produced there since the Roman era. The region is known for its Merlot, which was introduced in the early 20th century. Geographically the wine region is located on the south side of the Alps and includes the canton of Ticino and the neighbouring district of Moesa (Misox and Calanca valleys) in the canton of the Grisons, both areas being Italian-speaking. It is the warmest region of the country, olive oil is also produced there. The terroir varies from acid soil in the northern part to limestone in the southern part. The top quality wines of the region have the appellation del Ticino DOC or ticinese DOC, sometimes linked with a VITI label, and the wines in the medium category use della Svizzera Italiana or nostrano. The first traces of grapes in Ticino are some pollens in sediments, starting from the neolithic. Notable diffusion of grapes by humans probably dates from the late Bronze Age to the entire Iron Age, and the grapes were probably located near the lakes. At the beginning of the Roman era there was already substantial cultivation of grapes, and production of wine probably started in this period, as shown in a sculpture on a Roman tomb found in Stabio. Until the 18th century, grapes were grown as a secondary product in extensive vineyards, from which light wines were produced, using a form of sharecropping. The wine was produced in some local varieties, of which only Bondola survived. They were mainly red wines, but some were mixtures of red varieties with some white varieties. Because of new grapes diseases (e.g. phylloxera), the canton government decided to give a new direction to the wine industry: they instituted the cattedra itinerante (moving chair) to teach modern viticulture and winemaking methods, and to substitute new high-value grapes for the local grapes. After a few years of studies and selections, in 1906 the canton decided to seed and recommended Merlot as the main variety of grapes for the canton.