Latgalians (, , modern ; variant translations also include Latgallians, Lettigalls or Lettigallians) were an ancient Baltic tribe. They likely spoke the Latvian language, which probably became the lingua franca in present-day Latvia during the Northern Crusades due to their alliance with the crusaders. Latgalians later assimilated into the neighbouring tribes, forming the core of modern Latvians. History The Latgalians were an Eastern Baltic tribe whose origin is little known. In the 5th and 6th centuries, they lived in the eastern part of present-day Vidzeme (west of the Aiviekste River), and later on in nearly all the territory of that region. In written sources, they are mentioned from the 11th century onward. In the first two decades of the 13th century, the (Western) Latgalians allied with German (mainly Saxon) crusaders. Their lands (the Eldership of Tālava, the Principality of Jersika and the Principality of Koknese) were incorporated into Livonia as vassal states. In the 11th century, Eastern orthodoxy started to spread in Latgalian lands from Polotsk and Pskov. In the 12th century, Latgalian lands and their rulers paid tribute to the dukes of Polotsk. During the Livonian crusade in the 13th century, Latgalian elders switched from Eastern orthodoxy to Roman Catholicism and became vassals of the Livonian Order. Because of the crusade, many regions of Semigallia and Courland were left depopulated. Thus, part of the Latgalians migrated to those regions both during and after the war. Subsequently, between the 13th and 16th centuries, they gradually assimilated into the other Baltic tribes: the Selonians, the Semigallians and the Curonians. These formed the core of present-day ethnic Latvians. Archaeological data In the lands inhabited by Western and the Eastern Latgalians, about 80 flat cemeteries of Western Latgalian origin have been excavated, with more than two thousand burials uncovered. The first large scale excavations took place in Ludza Odukalns Cemetery in Latgale (1890–1891), where 339 Late Iron Age burials were uncovered. In the excavations at Pildas Nukši Cemetery (in Latgale, 1947–1948), 218 burials were uncovered, dated to the 9th to 12th centuries. At the Zvirgzdenes Kivti Cemetery (in Latgale: 1948, 1955–1958), 175 burials from the 7th to 12th centuries were excavated. 315 burials were found at Aglonas Kristapiņi Cemetery (in Latgale; 1928, 1938, 1977–1980, 1984–1987, 1999–2000), in use from the late 8th century to the 12th century. Ērgļu Jaunāķēni Cemetery was totally excavated in 1971–1972, with 89 burials found. At Koknese Cemetery, 102