historical region and realm comprising a vast territory now lying in northeastern Iran, southern Turkmenistan, and northern Afghanistan. The historical region extended, along the north, from the Amu Darya (Oxus River) westward to the Caspian Sea and, along the south, from the fringes of the central Iranian deserts eastward to the mountains of central Afghanistan. Arab geographers even spoke of its extending to the boundaries of India.

The history of the area stretches back to very ancient times, being part of the Achaemenid empire of the 6th and 5th centuries BC and the Parthian empire of the 1st century BC. (Khorāsān is sometimes loosely identified synonymously with Parthia.) Khorāsān was first named, however, by the Sāsānians (Sāsānian dynasty) (beginning in the 3rd century BC), who organized their empire into four quarters (named from the cardinal points), Khorāsān being literally the “Land of the Sun.” After the Arab conquest in AD 651–652, the name was retained both as the designation of a definite province and in a looser sense. At first the Arabs used the area as a march, or garrisoned frontier, but soon large colonies of Arabs moved in, especially around Merv, and a meld of Islāmic and eastern Iranian cultures ensued. Later Khorāsān regained virtual independence under the Ṭāhirid, Ṣaffārid, and Sāmānid dynasties (821–999). Successively it formed part of the Ghaznavid, Seljuq, and Khwārezm-Shāh kingdoms but was overrun by Genghis Khan in 1220 and again by Timur (Tamerlane) about 1383. The Iranian Ṣafavid kings (1502–1736) fought over it against Uzbek invasions. It was occupied by the Afghans from 1722 to 1730. Nāder Shāh, born in Khorāsān, broke the Afghan supremacy and made Meshed the capital of his Iranian empire. Ferdowsī, author of the Shāh-nāmeh (“Book of Kings”), and Omar Khayyam, the celebrated poet and sage, were born in the region. Khorāsān's current Iranian frontiers were defined in 1881 and in a convention of July 8, 1893.

Khorāsān, as a result of its troubled history, is peopled by a great variety of ethnic groups: Turkmen in the northwest; Kurds around Bojnūrd and Qūchān; Tīmūrīs and Jamshīdīs (Chahar Aimak) in the east, some of whom are still nomadic; farther southwest, Ḥeydarīs; and southeast, Baloch. The highlands in the south are home to a settled population of old Iranian stock. Here and there are found Berberis of Mongol origin, Arabs, Roma (Gypsies), and a few Jews in the towns. The largest cluster of settlements and cultivation stretches around the city of Meshed northwestward, containing the important towns of Qūchān, Shīrvān, and Bojnūrd. The languages spoken in Khorāsān are Turkish, Persian, and Kurdish.

In its physical geography, the northern part of Iranian Khorāsān contains two parallel ranges: an eastern prolongation of the Elburz Mountains and an independent ridge, the Koppeh Dāgh. Limestones and igneous and metamorphic rocks prevail; peaks include Kūh-e Hazār Masjed (10,321 feet 【3,146 m】) and Kūh-e Bīnālūd (10,536 feet 【3,211 m】). A great salt desert, Dasht-e Kavīr, with quicksandlike marshes, enters Khorāsān from the west. Sand dunes are widespread. There are many oases, large and crowded in the north but small and isolated in the south. The southern highlands, which are known as Kūhestān, have peaks reaching 7,000–9,000 feet (2,100–2,700 m). The climate is cool in the summer and cold in the winter. The north and northwest have sufficient rainfall for grasslands and scrub forests of alder, oak, juniper, and hornbeam; the south has little vegetation. Khorāsān's only permanent rivers are the Atrak, the Kal-e Mūreh, the Rūd-e Shūr, and the Kashaf Rūd, all more or less salty in their lower courses.

Modern Iranian Khorāsān is largely agricultural, producing fruits, cereals, cotton, tobacco, oil plants, saffron, and some silk. Livestock are plentiful; wool, lambskins, and goat hair are exported, and poultry is also raised. The mineral products include turquoise, salt, iron, copper, lead, zinc, chromium, magnesite, and coal. Cement, processed foods, ginned cotton, carded wool, sugar, pharmaceuticals, animal fodder, and textiles are the manufactured products. Handicrafts include jewelry, rugs and carpets, furs, dolls, glassware, and handloomed cloth. A railway and roads link Meshed, a thriving city, with Iran's capital, Tehrān.