Greater Khorasan contained mostly Nishapur, Tus (now in Iran), Herat, Balkh, Kabul and Ghazni (now in Afghanistan), Merv (now in Turkmenistan), Samarqand, Bukhara and Khiva (all now in Uzbekistan), Khujand and Panjakent (now in Tajikistan).
These days, the adjective greater is partly used to distinguish it from Khorasan province, in modern-day Iran, that forms western parts of these territories, roughly half in area . It is also used to indicate that Greater Khorasan encompasses territories that were perhaps called by some other popular name when they were individually referred to. For example Transoxiana (covered Uzbekistan and Tajikistan), Bactria, Kabulistan , Khwarezm (containing Samarkand and Bukhara) .
Until the devastating Mongol invasion of the thirteenth century, Khorasan was considered the cultural capital of Persia. (Lorentz 1995)
According to Mir Ghulam Mohammad, Afghanistan's current territories formed the major part of Khorasan. According to these latter sources, Khorasan province of Iran roughly comprises half of Greater Khorasan. Khorasan's boundaries have varied greatly during ages. The term was loosely applied to all territories of Persia that lay east and north east of Dasht-e Kavir and therefore were subjected to change as the size of empire changed.
In the Middle Ages, Persian Iraq and Khorasan were the two most important parts of the territory of Greater Iran. The dividing region between these two was mostly along with Gurgan and Damaghan cities. Especially the Ghaznavids, Seljuqs and Timurids, divided their Empire to Iraqi and Khorasani regions. This point can be observed in many books such as "Tārīkhi Bayhaqī" of Abul Fazl Bayhqi, Faza'ilul al-anam min rasa'ili hujjat al-Islam (a collection of letters of Al-Ghazali) and other books.
Ghulam Mohammad Ghubar, a historian from Afghanistan, talks of Proper Khorasan and Improper Khorasan in his book titled "Khorasan. According to him, Proper Khorasan contained regions lying between Balkh (in the East), Merv (in the North), Sijistan (in the South), Nishapur (in the West) and Herat, known as The Pearl of Khorasan, in the center. While Improper Khorasan's boundaries extended to Kabul and Ghazni in the East, Sistan and Zabulistan in the South, Transoxiana and Khwarezm in the North and Damaghan and Gurgan in the West.
In Memoirs of Babur, it is mentioned that Indians called non-Hindustanis (non-Indians) as Khorasanis. Regarding the boundary of Hindustan and Khorasan, it is written: "On the road between Hindustān and Khorasān, there are two great marts: the one Kābul, the other Kandahār." 1 Thus, Improper Khorasan bordered Hindustan (old India).
Greater Khorasan is one of the regions of Greater Iran. Before being conquered by Alexander the Great in 330 BC, it was part of the Achaemenid and Median Persian Empire. In 1st century AD, the eastern regions of Greater Khorasan fell into the hands of the Kushan empire. The Kushans introduced to a high grade Buddhist culture (though they were also Zoroastrians) to these regions and from where Buddhism began to spread by Khorasanian monks to China and even to Japan. Numerous Kushanian fire temples and Buddhist temples and buried cities with treasures in the northern and central areas of Khurasan (nowadays mainly Afghanistan) have been found. However the western parts of Greater Khorasan remained predominantly Zoroastrian as one of the three great fire-temples of the Sassanids "Azar-burzin Mehr" is situated in the western regions of Khorasan, near Sabzevar in Iran. The boundary was pushed to the west towards the Persian Empire by the emigrating Kushans. The boundary kept changing until the demise of the Kushan Empire where Sassanids took control of the entire region by conquering and merging with the Kushans (Kushano-Sassanian civilization). In Sassanid era, Persian empire was divided into four quarters, "Xwawaran" meaning west, apAxtar meaning north, Nīmrūz meaning south and Xurasan (Khorasan) meaning east. The Eastern regions saw again some conflict with Hephthalites who became new ruler of entire Khorasan but also for a short time of the entire Iranian plateau, but the borders remained much stable afterwards until the Muslim invasion.
Being the eastern parts of the Sassanid empire and further away from Arabia, Khorasan quarter was conquered in the later stages of Muslim invasions. In fact the last Sassanid king of Persia, Yazdgerd III, moved the throne to Khorasan following the Arab invasion in the western parts of the empire. After the assassination of the king, Khorasan was conquered by the Islamic troops in 647. Like other provinces of Persia it became one of the provinces of Umayad dynasty.
The first liberal movement against the Arab invasions was led by Abu Muslim Khorasani between 747 and 750. He helped the Abbasids come to power but was later killed by Al-Mansur, an Abbasid Caliph. The first independent kingdom from Arab rule was established in Khorasan by Tahir Phoshanji in 821. But it seems that it was more a matter of political and territorial gain. In fact Tahir had helped the Caliph subdue other nationalistic movements in other parts of Persia such as Maziar's movement in Tabaristan.
The first dynasty in Khorasan, after the introduction of Islam, was the Saffarid dynasty (861-1003). Other major dynasties in Khorasan were Samanids (875-999), Ghaznavids (962-1187), Ghurids (1149-1212), Seljukids (1037-1194), Khwarezmids (1077-1231) and Timurids (1370-1506). It should be mentioned that some of these dynasties were not Persian by ethnicity, nonetheless they were the advocates of Persian language and were praised by the poets as the kings of Iran.
Among them, the periods of Ghaznavids of Ghazni and Timurids of Herat are considered as one of the most brilliant eras of Khorasan's history. During these periods, there was a great cultural awakening. Many famous Persian poets, scientists and scholars lived in this period. Numerous valuable works in Persian literature were written. Nishapur, Herat, Ghazni and Merv were the centers of all these cultural developments. Some eastern Khorasani regions were then parts of the Moghul Empire, while the Safavids conquered the western regions. For Moghuls, Khorasan was always a region with great economic and cultural importance.