Lithuanian (lietuvių kalba) is the official state language of Lithuania and is recognized as one of the official languages of the European Union. There are about 3.2 million native Lithuanian speakers in Lithuania and about 200,000 abroad. Lithuanian is a Baltic language, closely related to Latvian, although they are not mutually intelligible. It is written in a Latin alphabet. The Lithuanian language is often said to be the most conservative living Indo-European language, retaining many features of Proto-Indo-European now lost in other Indo-European languages.
Among Indo-European languages, Lithuanian is an extraordinarily conservative, retaining many archaic features otherwise found only in ancient languages such as Sanskrit or Ancient Greek. For this reason, it is one of the most important sources in the reconstruction of the Proto-Indo-European language despite its late attestation (with the earliest texts dating only to c. 1500 AD). The phonology and especially the nominal morphology of Lithuanian is almost certainly the most conservative of any living Indo-European language, although its verbal morphology is less conservative, and may be exceeded by the conservatism of Modern Greek verbs, which maintain a number of archaic features lacking in Lithuanian, such as the synthetic aorist and mediopassive forms.
Lithuanian and other Baltic languages passed through a Proto-Balto-Slavic stage, from which Baltic languages retain numerous exclusive and non-exclusive lexical, morphological, phonological and accentual isoglosses in common with the Slavic languages, which represent their closest living Indo-European relatives. Moreover, with Lithuanian being so archaic in phonology, Slavic words can often be deduced from Lithuanian by regular sound laws.
According to some glottochronological speculations the Eastern Baltic languages split from the Western Baltic ones between AD 400 and AD 600. The Greek geographer Ptolemy had already written of two Baltic tribe/nations by name, the Galindai and Sudinoi (Γαλίνδαι, Σουδινοί) in the 2nd Century A.D. The differentiation between Lithuanian and Latvian started after AD 800; for a long period they could be considered dialects of a single language. At a minimum, transitional dialects existed until the 14th or 15th century, and perhaps as late as the 17th century. Also, the 13th- and 14th-century occupation of the western part of the Daugava basin (closely coinciding with the territory of modern Latvia) by the German Sword Brethren had a significant influence on the languages' independent development.
The earliest surviving written Lithuanian text is a translation dating from about 1503–1525 of the Lord's Prayer, the Hail Mary, and the Nicene Creed written in the Southern Aukštaitijan dialect. Printed books existed after 1547, but the level of literacy among Lithuanians was low through the 18th century and books were not commonly available. In 1864, following the January Uprising, Mikhail Muravyov, the Russian Governor General of Lithuania, banned the language in education and publishing, and barred use of the Latin alphabet altogether, although books printed in Lithuanian continued to be printed across the border in East Prussia and in the United States. Brought into the country by book smugglers despite the threat of stiff prison sentences, they helped fuel a growing nationalist sentiment that finally led to the lifting of the ban in 1904.