Riga was founded in 1201, and its official establishment by Albert, the third Bishop of Livonia, was due to the requirements of canon law, which mandated that a bishopric’s seat be located in a city. The previous seat of the diocese, Üxküll, situated on a small island in the Dvina River approximately 30 km from its mouth into the Gulf of Riga, did not meet this condition. In its initial phase, Riga was primarily a port, serving not only merchant ships with goods. Above all, it served pilgrims (crusaders) who arrived after the opening of navigation in the Baltic Sea following Easter for a year-long stay, hoping to benefit from plenary indulgence for participating in battles against pagans. Throughout the thirteenth century, Riga was the most important departure point for military expeditions against pagans and potential apostates. Sometimes, the city became the target of attacks by the indigenous population, especially dangerous in winter, when the Dvina was crossed by the Lithuanians and Semigallians. The river also facilitated (not always peaceful) contacts with the Rus’ Principality of Polotsk.