Lithuanian is sometimes referred to as an ‘open-air museum’. Its archaic features and similarities to Old Greek, Latin, or Sanskrit (a classical language of India) were noticed in the nineteenth century with the rise of comparative-historical linguistics. Linguists believe Lithuanian is most related to the Proto-Indo-European language. It has retained long and short vowels (like Old Greek), vowels at the end of a word, and free accent (like Sanskrit). From other Indo-European language Lithuanian also differs by its vocabulary.

According to researchers, people who spoke this proto-language spread in all directions from the original homeland of Indo-Europeans. This was how the Proto Indo-European language gradually changed and differentiated, giving birth to multiple Indo-European languages, e.g. Spanish, Italian, Portuguese, Russian, Polish, Czech, English, German, Swedish, Danish, Lithuanian, Latvian, and many others.

The French linguist Anoine Meillet once said that ‘him who is eager to know how our great grandfathers (Indo-Europeans) used to speak should come and listen to a Lithuanian peasant talking’. Meillet studied Indo-European languages, visited Lithuania several times, and kept in touch with the Lithuanian linguist Kazimieras Būga.