As early as the 8th century BC, Aramaic language and writing competed with the East Semitic Akkadian language and script (cuneiform) in Assyria, and thereafter it spread throughout the Orient. By around 500 BC, Aramaic had become the lingua franca of the Achaemenid Empire. Although marginalized by Greek in the Hellenistic period, it remained unchallenged as the common dialect of all peoples of the region until the Islamic conquest of Mesopotamia in the 7th century AD.