With the rise of the Umayyad Caliphate, the designation was inherited and likewise stretched as far as their military gains in the east, starting off with the military installations at Nishapur and Merv, slowly expanding eastwards into Tokharistan and Sogdia. Under the Caliphs, Khorasan was the name of one of the three political zones under their dominion (the other two being Eraq-e Arab Arabic Iraq and Eraq-e Ajam Non-Arabic Iraq or Persian Iraq). Under the Umayyad and Abbasid caliphates, Khorasan was divided into four major sections or quarters (rub′), each section based on a single major city: Nishapur, Merv, Herat and Balkh. By the 10th-century, Ibn Khordadbeh and the Hudud al-'Alam mentions what roughly encompasses the previous regions of Abarshahr, Tokharistan and Sogdia as Khwarasan proper. They further report the southern part of the Hindu Kush, i.e. the regions of Sistan, Ghor, Rukhkhudh, Zabulistan and Kabul etc. to make up the Khwarasan marches, a frontier region between Khwarasan and Hindustan which at the time would have been in a process of Islamization.