Selonia (; ), also known as Augà ¡zeme (the "Highland"), is one of the Historical Latvian Lands as well as a portion of northeastern Lithuania. Its main city and cultural center is JÃÂkabpils. The Selonian language has become extinct, though some of the inhabitants still speak a .
The territory of Selonia is defined by Latvian law as follows: Aizkraukle Municipality (the part of Aizkraukle city on the left bank of the Daugava, Daudzese Parish, Jaunjelgava Parish, Jaunjelgava city, Nereta Parish, Mazzalve Parish, Pilskalne Parish, Sece Parish, SÃÂrene Parish, Staburags Parish, SunÃÂkste Parish, Zalve Parish), Augà ¡daugava Municipality (Bebrene Parish, Demene Parish, Dviete Parish, Eglaine Parish, Ilà «kste city, Kalkà «ne Parish, Laucesa Parish, Medumi Parish, Pilskalne Parish, Prode Parish, Saliena Parish, Skrudaliena Parish, Subate city, Svente Parish, à  ÃÂdere Parish, Tabore Parish, Vecsaliena Parish), the part of Daugavpils city on the left bank of the Daugava, JÃÂkabpils Municipality (Aknëste Parish, Aknëste city, Asare Parish, ÃÂbeüi Parish, DignÃÂja Parish, Dunava Parish, Elkà ¡à Âi Parish, GÃÂrsene Parish, the part of JÃÂkabpils city on the left bank of the Daugava, Kalna Parish, Leimaà Âi Parish, Rite Parish, Rubene Parish, Sala Parish, Sauka Parish, SÃÂlpils Parish, Viesëte city, Viesëte Parish, Zasa Parish) and KrÃÂslava Municipality (Kaplava Parish, the part of the city of KrÃÂslava on the left bank of the Daugava).
The subjugation and baptism of the Selonians started in 1208, when Albert of Buxhoeveden captured SÃÂlpils hillfort (). The term "Selonians" is most probably the German adaptation of the Livonian name "Highlanders", which leads to the hypothesis that the Selonians and Aukà ¡taitians belonged to the same ethnos. The Livonian Chronicle of Henry describes the Selonians as allies of the Lithuanians. In 1218 the region formed a Selonian diocese, but in 1226 part of that diocese was joined to the Riga archbishopric and the Bishopric of Semigalia was formed. During the Lithuanian wars with the Livonian Brothers of the Sword and from 1237 the Livonian Order, Selonia became partially deserted. From the 14th to the mid-16th centuries, the southern part of the former Selonia belonged to the Grand Duchy of Lithuania, while the northern part was ruled by the Livonian Order; after the latter collapsed in 1561, it fell to the Duchy of Courland, a vassal of the Grand Duchy of Lithuania.
Nowadays the region is mainly inhabited by Latvians with large ethnic minorities of Russians, Poles, Belarusians and Lithuanians in the southeastern municipality of Augà ¡daugava Municipality.
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. Their boundary went from the Daugava at Naujene, near Daugavpils castle, running along Kopkelis to Luodis lake and northwards along the Duseta river to lake Sartai and towards the source of the à  ventoji. It stretched further to the Latuva, Vaà ¡uoka and Vieà ¡inta rivers, along the LÃÂvuo river northwards to the Mà «à ¡a (Mà «sa) and downstream, to the mouth of the Babëte (Bà «ga, 1961, p. 273âÂÂ274).
Thus, the historical sources describing the Selonian boundaries in the second half of the 13th century are rather precise. The linguist Kazimieras Bà «ga, basing himself on linguistic data alone, specifies the southern boundary of the Selonian territory as running approximately by the towns of Salakas, Tauragnai, Utena, SvÃÂdasai, SubaÃÂius, PalÃÂvenÃÂ, Pasvalys, and SaloÃÂiai. Regional history museum of the Selonia region of Lithuania, founded in 1928 in Birà ¾ai Castle.