Proto-Armenian, as the common ancestor of only one language, has no clear definition of the term. It is generally held to include a variety of ancestral stages of Armenian between Proto-Indo-European and the earliest attestations of Classical Armenian.
It is thus not a proto-language in the strict sense, but "Proto-Armenian" is a term that has become common in the field.
The earliest testimony of Armenian is the 5th-century Bible translation of Mesrop Mashtots. The earlier history of the language is unclear and the subject of much speculation. It is clear that Armenian is an Indo-European language, but its development is opaque.
In any case, Armenian has many layers of loanwords and shows traces of long language contact with Indo-Aryan Mitanni, Anatolian languages such as Luwian and Hittite, Semitic languages such as Akkadian and Aramaic, and the Hurrio-Urartian languages.