Henry of Livonia wrote about an encounter between the Oeselian pagans and a captured Christian missionary, Frederick of Zelle, during the 13th century. The Oeselians are quoted using the words "Laula! Laula! Pappi!" when torturing the missionary. This Finnic expression has been suggested to support the identification of Oeselians as a Finnic language group at that time. In 1206, the Danish army led by king Valdemar II and Andreas, the Bishop of Lund landed on Saaremaa and attempted to establish a stronghold without success. In 1216 the Livonian Brothers of the Sword and the bishop Theodorich joined forces and invaded Saaremaa over the frozen sea. In return the Oeselians raided the territories in Latvia that were under German rule the following spring. In 1220, the Swedish army led by king John I of Sweden and the bishop Karl of Linköping conquered Lihula in Rotalia in Western Estonia. Oeselians attacked the Swedish stronghold the same year, conquered it and killed the entire Swedish garrison including the Bishop of Linköping. In 1222, the Danish king Valdemar II attempted the second conquest of Saaremaa, this time establishing a stone fortress housing a strong garrison. The Danish stronghold was besieged and surrendered within five days, the Danish garrison returned to Reval, leaving bishop Albert of Riga' brother Theodoric and few others behind hostages as pledges for peace. The castle was leveled to the ground by Oeselians. In 1227, the Livonian Brothers of the Sword, and Bishop Albert of Livonia organized a combined attack against Saaremaa. After the destruction of Muhu Stronghold and surrender of Valjala Stronghold, the Oeselians formally accepted Christianity. In 1236, after the defeat of the Livonian Brothers of the Sword in the Battle of Saule, military action on Saaremaa broke out again. Oeselians accepted Christianity again by signing treaties with the Livonian Order's Master Andreas de Velven and the Bishopric of Ösel-Wiek in 1241, setting penalties for pagan rituals. The next treaty was signed in 1255 by the Master of the Order, Anno Sangerhausenn, and, on behalf of the Oeselians, by elders whose "names" (or declaration?) had been phonetically transcribed by Latin scribes as Ylle, Culle, Enu, Muntelene, Tappete, Yalde, Melete, and Cake.