Üxküll (mod. Ikšķile, Latvia) was a site on the river Düna some 28 kilometers (17 mi.) upstream from Riga. It became the earliest center of missionary activity in medieval Livonia.
The first known missionary in Livonia, an Augustinian canon from Segeberg named Meinhard (d. 1196), settled there with some German merchants in the 1180s, erecting a church on the site of an older stone building, and began to preach Christianity to the Livic inhabitants. In about 1185, Meinhard had a castle built at Üxküll by masons from Gotland, the first stone fortress in Livonia. Together with another castle on the island of Holme, Üxküll was important in securing commerce on the waterway between Russia and the West. In 1186 Meinhard was named bishop of Üxküll by Hartwig II, archbishop of Hamburg-Bremen.
The bishopric remained at Üxküll until it was moved downstream to the newly established town of Riga by Bishop Albert of Buxhovden in 1201, probably because of better connections overseas.Üxküll was subsequently enfeoffed to members of the German nobility in Livonia. The castle itself remained small and was ruined in the seventeenth century.