In its time Venice has exerted considerable and sometimes lasting influence on the wines of the world. Medieval Venice had no agriculture or viticulture and obtained its wine and grain from lombardy to the west; Venice’s importance was in its trade. In 840 a treaty, known as the Pactum Lotharii, between charlemagne’s grandson Lothair and the doge of Venice, protected Venice’s neutrality and guaranteed its security from the mainland. This treaty made Venice independent from the west and from Byzantium. Thus Venice became the most important of the Italo-Byzantine ports, and its position was strengthened when the Byzantines discovered that Venice’s rivals Amalfi, naples, and Gaeta had been collaborating with the Saracens. Initially Venice owed its wealth to its trade, acquiring possession of Crete, Modon, and Coron in the Aegean and being granted exemptions from the taxation in Constantinople that was to ruin the Byzantine economy (see greece, medieval history). The Crusades only strengthened Venice’s position at the frontier between northern Europe and the eastern Mediterranean.