LTReikšminiai žodžiai: Neris; Vilija; Upės; Neris; Vilija; Rivers.
ENOne of the most important issues of the Neris history not solved so far is related to two names of the river used in parallel. In the 19th century, the subject of the dual name of the river was investigated primarily taking into consideration a historical background, and in the 20th century, linguistics was taken into account. A complex view, evaluating linguistic, archaeological, historical and partly ethnographical data, allows us to correct the conclusions drawn so far. The Vilija / Neris is a river 510 km long, which considerably changes its appearance several times: the width of the valley and river bed, the swiftness of the stream, the inclination, and the steepness of the banks. One part of the Vilija / Neris is called "marshy", and it flows through marshy flooded meadows (down the river up to Smorgon). The other part of the river is called "stony", and it erodes through the hills of the Ašmena. In both of these river sections (the first is about 180 km long, while the second - 330 km), different fish spawn and various types of boats were used. Changes in dialect and some other differences of material culture form the boundary between these two regions. The barrows in the eastern part of Lithuania are low soil mounds, surrounded by stone circles - in the 3rd-5th centuries they spread in the western part of the Vilija / Neris basin. In the eastern part (in the upper reaches of the Vilija / Neris), deserting hill forts of Striated Ware culture, people settled in open settlements typical of Bancerov culture. Approximately in the 6th c., the margin started to become clear dividing archaeological cultures in the strip of Narutis Lake (Byelorussian: Нарачь) - the Naročia River (Byelorussian: Нарачанка). And later, approximately in the 9th-12th centuries, the range of barrows of east Lithuanian type remained hardly changed, and in the upper reaches of the Vilija / Neris, the barrows typical of Polotsk Krivitchi prevailed.In 1857, during the expedition, Count Konstanty Tyszkiewicz first heard the name Neris from the inhabitants of Grabijolai village, i. e. having sailed along the river more than 360 km. The historical toponyms recorded on the banks of the Vilija / Neris allow us to draw this situation more exact and show that in the past, the name Neris was used everywhere, where, according to the data of the 19th c., people used to speak Lithuanian. However, in the 15th-19th c., in the region of the upper reaches of the Vilija / Neris (up to its confluence with the Naročia), historical documents did not record anything reminding of the name of the Neris. As there was no hint of the usage of the name Neris up the river from its confluence with the Naročia, one has to remember the assumption made by Professor Steponas Kolupaila in 1940. He found out that ancient Lithuanians had regarded the Naročia as the very beginning of the Neris, flowing out from Narutis Lake. The Vilija was considered the left tributary of the Neris in this instance! The semantic relation of the hydronym Narutis (in the Lithuanian language) or Naročius (already slavianized form) with the Neris does not raise great doubts. The naming model, when a lake and the river flowing from it have related names, is well known, too. However, would the Vilija twice as long as the Naročia is and having much more water, have been regarded only the left tributary of the Naročia (and according to S. Kolupaila-of the Neris)? The complex view gives the conclusion that in the past, the river was called the Neris from the confluence of the rivers - the Vilija and the Naročia. At the joint of the two cultural regions in the aforementioned area between Narutis Lake in the north and Smorgon in the south, such a case seems very possible. The origination of a new name of a river, when two rivers that are called differently flow in together, is known.For instance, such is the Nemunas, whose name is started to use when the Usa and the Losa flow in together, such is the Lielupė (flows into the Gulf of Riga), originating when the Mūša and the Nemunėlis flow in together. So, the data that are possessed today show that the name Vilija (