The Selonians (Latvian: sēļi; Lithuanian: sėliai, from Livonian: sälli – "highlanders") were a tribe of Baltic peoples.They eventually merged with neighbouring tribes, contributing to the ethnogenesis of modern Latvians and Lithuanians.Archeological data can trace the Selonians back to the beginning of 1st millennium AD when they lived on both sides of the Daugava River.Some scholars speculate that during the late Iron Age the Selonians had already partly merged with the Latgalians.In 1207, the German Brothers of Sword together with their Livonian and Latgalian allies besieged the main Selonian centre at Sēlpils hillfort.