town of Tabas, known as "the Gate of Khorasan", from which it extended eastward to the mountains of central Afghanistan. Sources from the 10th century onwards refer to areas in the south of the Hindu Kush as the Khorasan Marches, forming a frontier region between Khorasan and Hindustan. Geography First established in the 6th century as one of four administrative (military) divisions by the Sasanian Empire, the scope of the region has varied considerably during its nearly 1,500-year history. Initially, the Khorasan division of the Sasanian Empire covered the northeastern military gains of the empire, at its height including cities such as Nishapur, Herat, Merv, Faryab, Taloqan, Balkh, Bukhara, Badghis, Abiward, Gharjistan, Tus and Sarakhs. 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, Rukhkhudh, Zabulistan and Kabul etc. to make up the Khorasan marches, a frontier region between Khorasan and Hindustan.By the late Middle Ages, the term lost its administrative significance, in the west only being loosely applied among the Turko-Persian dynasties of modern Iran to all its territories that lay east and north-east of the Dasht-e Kavir desert. It was therefore subjected to constant change, as the size of their empires changed. In the east, Khwarasan likewise became a term associated with the great urban centers of Central Asia. It is mentioned in the Memoirs of Babur that: In modern times, the term has been source of great nostalgia and nationalism, especially amongst the Tajiks of Central Asia. Many Tajiks regard Khorasan as an integral part of their national identity, which has preserved an interest in the term, including its meaning and cultural significance, both