Curonian language
Curonians (or Kurshes) were one of Lettish tribes which lived near the Baltic Sea along the modern Lithuanian coast. They are well known from the history of Middle Ages. As they inhabited shores they began to suffer foreign invasions already in the 7th century, mainly by Vikings who did not want to occupy lands but were just hunting for gold and goods. In the 7th and 8th century Curonians needed to contain Viking aggression very often, but all attacks were repelled, and Curonians kept their independence.

They did not have a state, cities or kings. Their religion was paganism, and as there is no mountains in the region where they could hold religious rituals, Curonians used to make hills themselves. Those hills, many of which are still seen in West Lithuania, are more widely known as Curonian defense measure. In the 12th century, German Teutonic knights came to Baltic region willing to make tribes take up Christianity. Curonians used their hills to warn each other about the coming invaders. Usually it was a priest who was in charge of the fire on the top of a hill.

But still Curonian lands were conquered by Teutonic knights, and later, in the 15th century, came under Lithuanian Principality rule. In the 17th century Curonian language disappeared, assimilated by Lithuanian. But even now dialects of Western Lithuania remind us about the language. It was supposedly more archaic and conservative than Lithuanian or Latvian, but in most features was similar to them - the same structure of declension (with just maybe eight cases instead of classical seven in Lithuanian), the same verb and verbal noun forms (participles, semi-participles, infinitive and supine). Its similarity to Lithuanian was one of the reasons for its fast assimilation.