Transoxiana (also spelled Transoxania) is the ancient name used for the portion of Central Asia corresponding approximately with modern-day Uzbekistan, Tajikistan, southern Kyrgyzstan and southwest Kazakhstan. Geographically, it is the region between the Amu Darya (Ancient Greek: Ώξος Ōxos) and Syr Darya rivers. When used in the present, it usually implies that one is talking about that region in the time prior to about the 8th century, although the term continued to remain in use among western historians for several centuries after. In the Persian epic Shahnameh, written by the poet Ferdowsi, Transoxiana is the homeland of the Iranian nomadic tribes and the Oxus river is the border between Iran and Turan.
The region was one of the satrapies of the Achaemenid dynasty of Persia under the name Sogdiana. Transoxiana, however, is Latin, and literally means "across the Oxus River", the Greek name for the Amu Darya, which describes the region perfectly from the viewpoint of the Greeks and Romans. The area was called prdry and Faraa-rood in Middle Persian, the latter means "that which is beyond the river". After invasion of Arabs they called it mā warā' an-nāhr which is a translation of the Mid. Persian name and has the same meaning, and is an alternative name for the country, and is also rendered Mawarannahr.
The name Transoxiana stuck in Western consciousness because of the exploits of Alexander the Great, who extended Greek culture into the region with his conquests of the 4th century BC; Transoxiana was the most north-eastern point of the Hellenistic culture, and in fact kept a hybrid Greek/Indian/Persian/Chinese culture, dubbed 'Serindian', until the Arabic invasion. During the Sassanid Empire, it was often called Sogdiana, a provincial name taken from the Achaemenid Empire, and used to distinguish it from nearby Bactria.
The Chinese explorer Zhang Qian, who visited the neighbouring countries of Bactria and Parthia along with Transoxiana in 126 BC, made the first known Chinese report on this region. Zhang Qian clearly identifies Parthia as an advanced urban civilisation that farmed grain and grapes, made silver coins and leather goods. It was ruled successively by Seleucids, Greco-Bactrian Kingdom, Parthian Empire and Kushan Empire before Sassanid rule.
In Sassanid times, the region became a major cultural and scientific centre due to effective royal authority and the wealth derived from the Northern Silk Road. Sassanid rule was interrupted by Hephthalite invasion at end of 5th century and didn't return to Sassanids till 565. Many Persian nobles and landlords escaped to this region after the Muslim invasion. Before the Muslim invasion it was also ruled by Gokturks. Following the Arab conquest, the area became known as Ma wara'un-Nahr (Arabic, "what is beyond the river").
Transoxiana's major cities and cultural centres are Samarkand and Bukhara. Both are in the southern portion of Transoxiana, (though still to the north of the Amu Darya itself, on the river Zeravshan), and the majority of the region was dry but fertile plains. Both cities remained centres of Persian culture and civilisation after the Islamic conquest of Iran, and played a crucial role in the revival of Persian culture with establishment of the Samanid dynasty.
Part of this region was conquered by Qutayba ibn Muslim between 706 and 715 and loosely held by the Umayyads from 715 to 738. The conquest was consolidated by Nasr ibn Sayyar between 738 and 740, and continued under the control of the Umayyads until 750, when it was replaced by the Abbasids. The Tang Dynasty also controlled the eastern part of the region until about the same time, when a civil war occurred.
Genghis Khan invaded Transoxiana in 1219 during his conquest of Khwarezm. Before his death in 1227, he assigned the lands of Western Central Asia to his second son Chagatai, and this region became known as the Chagatai Khanate. In 1369, Timur, of the Barlas tribe, became the effective ruler while continuing the ceremonial authority of Chagatai Khan's dynasty, and made Samarkand the capital of his future empire. Transoxiana was known to be flourishing in the mid-14th century.
References and notes 
- Encyclopædia Britannica online
- "ضرورتها و هدفهای ترویج فرهنگ ایرانی در عهد سامانیان". (in Persian) رشد آموزش تاریخ (زمستان ۱۳۸۴): ش. ۲۱. ص. ۳۱.
- Silk Road, North China, C. Michael Hogan, The Megalithic Portal, ed. A. Burnham (2007)
- The Timurid Empire