Neris (, ) is a river arising in Belarus, flowing through Vilnius (Lithuania) and becoming a tributary of the Neman River (Nemunas) at Kaunas (Lithuania). Its length is 510 km.

275 km of the river runs through Belarus, where it is called Vilija, and 235 km runs through Lithuania, where it is called Neris.

The Neris connects two old Lithuanian capitals - Kernavė and Vilnius. Along its banks are burial places of the pagan Lithuanians. 25 km from Vilnius are the old burial mounds of Karmazinai. There also are many mythological stones, and a sacred oak.

Dual naming

The issue of the dual naming of the river as Neris by the Lithuanians and Vilija (formerly Velja, meaning "big, great" in Slavic) by the Slavs is complex. Even in Vilnius, there are toponyms including both names, e. g. Neris remains in the riverside names of Paneriai and Paneriškės while Velja is a part of the name Valakampiai, which means "an angle of Velja" in Lithuanian.Vykintas Vaitkevičius , Šiaurės Atėnai. 2005-07-23 nr. 758
Although it has been suggested that Neris is the primeval name of the river, while name Vilija is of a secondary extraction, the dual naming most probably emerged from the confluence of rivers Neris (now known as Narach River, leaving Lake Narach) and Velja, in the historical Slavic/Baltic borderland, each ethnos choosing their own name for the river starting at the confluence. It is moreover evidenced by the fact that the name Neris was never used to name the river Velja up to this confluence. Therefore it has been proposed that the Narach River had in fact been considered the upper reaches of Neris by the Balts in ancient times.

Etymology

The name Neris is of Baltic origin, a cognate of the Lithuanian nerti generally meaning "to dive, swim downstream" as well as "to net, crochet". It is likely that the name had a more general meaning of "flow" or particularly "swift and swirling flow" in early times.

Etymologically, the name is one of a class of hydronyms, widespread in the modern and prehistoric Baltic ranges; e. g. Lithuanian Narotis, Narasa (rivers), Narutis (lake), Old Prussian Narus, Nara near Moscow. These are related to Lithuanian narus, "deep", and nerti, "to dive".

More remote connections are obscure, although the root is believed to be Indo-European. There are a number of possibilities:

• Pokorny's 2nd *ner-, "under" (Indogermanisches etymologisches Wörterbuch, pp765–766);

• Derksen's *nerH-, o-grade *norH- (Slavic Inherited Lexicon);

• A relation to the Greek god Nereus, which may be from *snau-, "to give milk to", in the sense of "flow" (Partridge, Origins (1983)).