The Tajiks are an Iranian people, speaking a variety of Persian, concentrated in the Oxus Basin, the Farḡāna valley (Tajikistan and parts of Uzbekistan) and on both banks of the upper Oxus, i.e., the Pamir Mountains (Mountain Badaḵšān, in Tajikistan) and northeastern Afghanistan and western Afghanistan (Badaḵšān, Kābol, Herat, Balkh, Mazar-i-Sharif, Ghazni and other urban regions). Historically, the ancient Tajiks were chiefly agriculturalists before the Arab Conquest of Iran. While agriculture remained a stronghold, the Islamization of Iran also resulted in the rapid urbanization of historical Khorasan and Transoxiana that lasted until the devastating Mongolian invasion. Several surviving ancient urban centers of the Tajik people include Herat, Samarkand, Bukhara, Khujand, Termez, Balkh and Kabul.