[1] The name was first given to the eastern province of Persia during the Sasanian Empire[2] and was used from the Late Middle Ages in distinction to neighbouring Transoxiana.

[3][4][5] This province, whose people are mainly Shia Muslims,[6] roughly encompassed the western portion of the historical Greater Khorasan.

"sunrise"; "east"; or "land of the rising sun") was originally given to the eastern province of Persia during the Sassanian period.

Some of the main historical cities of Persia are located in the older Khorasan: Nishapur and Tus (now in Iran); Merv and Sanjan (now in Turkmenistan); Samarkand and Bukhara (both now in Uzbekistan); Herat and Balkh (now in Afghanistan); and Khujand and Panjakent (now in Tajikistan).

The largest cluster of settlements and cultivation stretches around the city of Mashhad northwestward, containing the important towns of Quchan, Shirvan, and Bojnurd.