The Baltic languages are of particular interest to linguists because they retain many archaic features, which are believed to have been present in the early stages of the Proto-Indo-European language. However, linguists have had a hard time establishing the precise relationship of the Baltic languages to other languages in the Indo-European family. Several of the extinct Baltic languages have a limited or nonexistent written record, their existence being known only from the records of ancient historians and personal or place names. All of the languages in the Baltic group (including the living ones) were first written down relatively late in their probable existence as distinct languages. These two factors combined with others have obscured the history of the Baltic languages, leading to a number of theories regarding their position in the Indo-European family.