[1] The subjugation and baptism of the Selonians started in 1208, when Albert of Buxhoeveden captured Sēlpils hillfort (Latin: castrum Selonum).

The Livonian Chronicle of Henry describes the Selonians as allies of the Lithuanians.

Among historical documents, the Mindaugas's Donation Act of 1261 is the one that best describes the transfer of the Selonian lands to the Knights of the Sword.

Thus, the historical sources describing the Selonian boundaries in the second half of the 13th century are rather precise.

The linguist Kazimieras Būga, basing himself on linguistic data alone, specifies the southern boundary of the Selonian territory as running approximately by the towns of Salakas, Tauragnai, Utena, Svėdasai, Subačius, Palėvenė, Pasvalys, and Saločiai.