The earliest testimony of the Armenian language dates to the 5th century AD (the Bible translation of Mesrob 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. The Graeco-Armenian hypothesis proposes a close relationship to the Greek language, putting both in the larger context of Paleo-Balkans languages (notably including Macedonian and Phrygian, which are widely accepted as Indo-European languages particularly close to Greek), consistent with Herodotus' recording of the Armenians as descending from colonists of the Phrygians.
In any case, Armenian has many layers of loanwords and shows traces of long language contact with Hurro-Urartian, Greek and Iranian.
The Proto-Armenian sound-laws are varied and eccentric (such as *dw- yielding erk-), and in many cases uncertain.
PIE voiceless stops are aspirated in Proto-Armenian, a circumstance that gave rise to the Glottalic theory, which postulates that this aspiration may have been sub-phonematic already in PIE. In certain contexts, these aspirated stops are further reduced to w, h or zero in Armenian (PIE *pots, Armenian otn, Greek pous "foot"; PIE treis, Armenian erek’, Greek treis "three").
The reconstruction of Proto-Armenian being very uncertain, there is no general consensus on the date range when it might have been alive. If Herodotus is correct in deriving Armenians from Phrygian stock, the Armenian-Phrygian split would probably date to between roughly the 12th and 7th centuries BC, but the individual sound-laws leading to Proto-Armenian may have occurred at any time preceding the 5th century AD. The various layers of Persian and Greek loanwords were likely acquired over the course of centuries, during Urartian (pre-6th century BC) Achaemenid (6th to 4th c. BC; Old Persian), Hellenistic (4th to 2nd c. BC Koine Greek) and Parthian (2nd c. BC to 3rd c. AD; Middle Persian) times.
“ The Armenians according to Diakonoff, are then an amalgam of the Hurrian (and Urartians), Luvians and the Proto-Armenian Mushki who carried their IE language eastwards across Anatolia. After arriving in its historical territory, Proto-Armenian would appear to have undergone massive influence on part the languages it eventually replaced. Armenian phonology, for instance, appears to have been greatly affected by Urartian, which may suggest a long period of bilingualism.