In the 4th century BC in the territory of historical Armenia, two administrative-political units were formed, Greater Armenia and Lesser Armenia, whose borders ran along the Western Euphrates River.
Greater Armenia included fifteen provinces (nahangs) – Ayrarat, Gugark, Utik, Artsakh, Syunik, Paytakaran, Parskahayk, Vaspurakan, Korchayk, Moghk, Aghdznik, Turuberan, Tsopk (Sophene), Upper Armenia, and Tayk. Each of the provinces was divided into several counties (gavars). The territory of Greater Armenia covered about 300,000 square kilometers at its greatest extent.
The territory of Lesser Armenia located to the west of the Euphrates was about 80,000 square kilometers.
The Armenian Highlands housed the crossroads of the most important trade routes of the ancient world that connected the East and the West. Two of them also linked Mesopotamia and the North Caucasus through Armenia.
The territory of the present-day Republic of Armenia covers about 30,000 sq. km and includes part of Ayrarat, Syunik, and Gugark, constituting 1/10 of the historical regions of Greater Armenia. The modern Republic of Artsakh also includes part of the historical regions of Artsakh, Utik, and Syunik.
Source: History of the Armenian people in questions and answers (Russian-Armenian (Slavic) University) armenia.ru