# Hexi Corridor

The Hexi Corridor (/həˈʃiː/ hə-SHEE), also known as the Gansu Corridor, is an important historical region located in the modern western Gansu province of China. It refers to a narrow stretch of traversable and relatively arable plain west of the Yellow River's Ordos Loop (hence the name Hexi, meaning 'west of the river'), flanked between the much more elevated and inhospitable terrains of the Mongolian and Tibetan Plateaus.
As part of the Northern Silk Road, running northwest from the western section of the Ordos Loop between Yinchuan and Lanzhou, the Hexi Corridor was the most important trade route in Northwest China. It linked China proper to the historic Western Regions for traders and military incursions into Central Asia. It is a string of oases along the northern edges of the Qilian Mountains and Altyn-Tagh, with the high and desolate Tibetan Plateau further to the south. To the north are the Longshou, Heli and Mazong Mountains separating it from the arid Badain Jaran Desert, Gobi Desert and the cold steppes of the Mongolian Plateau. At the western end, the route splits into three, going either north of the Tianshan Mountains or south on either side of the Tarim Basin. At the eastern end, the mountains around Lanzhou grants access to the Longxi Basin, which leads east through Mount Long along the Wei River valley into the populous Guanzhong Plain, and then into the Central Plain.

## Geography
### Location

The Hexi Corridor is located in western Gansu province, bordered to the south by the Qilian Mountains and to the north by the Gobi Desert. It extends for approximately 1,000–1,200 kilometres (620–750 mi) from Wushao Mountain in the south to Dunhuang in the north, and covers around 276,000 square kilometres (107,000 sq mi).
There are several major cities along the Hexi Corridor. From west to east, the major cities are: Dunhuang, Yumen, Jiayuguan, Jiuquan, Zhangye, Jinchang, Wuwei, and finally Lanzhou in the southeast. Just south of the provincial boundary of Gansu lies Xining, the capital of Qinghai Province, which served as the chief commercial hub of the Hexi Corridor along the Northern Silk Road.

## History
### Prehistory

The Hexi Corridor had been the site of east-west cultural exchanges across Eurasia since prehistory. It was first settled around 4800 BP in Neolithic times by millet farmers from the Yangshao Culture in the western Loess Plateau, who enabled the spread of millet to Central Asia and the rest of Eurasia and Africa. These farmers also had pottery production techniques from Northern China. Several cultures developed in the Hexi corridor during this time, such as the Majiayao, Banshan, and Machang.
The oldest bronze object to be discovered in China, dating to 5000-4500 BP, was found at the Majiayao site. However, none of the Neolithic cultures in the Hexi Corridor at this time possessed the technology to smelt bronze, and only two sites had any bronze at all. As such, the Bronze Age only began in the Hexi Corridor around 4200 BP with the arrival of smelting technology from Central Asia, and the production of bronze reached its peak around 4000-3500 BP. Domesticated livestock were also introduced to the area around this time; thus, these cultures typically farmed millet and wheat, while keeping livestock such as sheep, pigs, cattle and horses. Bronze age societies in the Hexi Corridor at this time include the Shajing, Qijia, Xichengyi, Siba, and Shanma cultures.
Wheat and barley from the Fertile Crescent arrived in the Hexi Corridor via Central Asia around 4000 BP, and later spread into China proper. By around 3700-3500 BP, most likely due to the continual weakening and retreat of the East Asian monsoon since 4000 BP which had caused increasing aridity, the more drought-resistant wheat and barley had replaced millet as the main staple crop in the Hexi Corridor. Cultures after this time period (such as the Shajing culture) saw a decrease in site numbers and bronze artifacts, and became dominated by nomadic production rather than agriculture.

### Xiongnu conquest

The Yuezhi were a nomadic tribe that lived in the Hexi Corridor, and were possibly associated with the Shajing culture. The Xiongnu were a nomadic people, centered around the Ordos Block near the Yellow River, who were subordinate to the Yuezhi. The Xiongnu were pushed out of their heartlands by the Qin dynasty in 215 BCE, and the Great Wall of China was constructed to enclose these conquered territories, which included parts of the Hexi Corridor. As a result of this defeat, the Xiongnu unified under Modu Chanyu into a confederacy against the Qin. Following the collapse of the Qin dynasty in 206 BCE, the Xiongnu reoccupied the captured territories.
In 176 BCE, the Xiongnu confederation under Modu Chanyu decisively defeated their previous overlords, the Yuezhi, while also subjugating twenty-six other tribes in the vicinity. This, combined with two more defeats at the hands of the Xiongnu under Modu's son Laoshang Chanyu, caused the westward escape of the majority of the Yuezhi survivors (later known as the Greater Yuezhi) from the Hexi Corridor, with the remaining population (the Lesser Yuezhi) mixing among the Qiang people south of the Hexi Corridor.

### Han incursions and occupation

After their expulsion of the Yuezhi, the Xiongnu were in complete control of modern-day Gansu, and by extension the Hexi Corridor. Around 138 BCE, during the reign of Emperor Wu of Han, diplomat Zhang Qian was sent to make contact with the Greater Yuezhi to convince them to ally with the Han dynasty against the Xiongnu, and for them to move back into their former lands in the Hexi Corridor. He was unsuccessful in doing so, and was captured and held by the Xiongnu on both his way to the Yuezhi and back, but was able to give detailed accounts of various kingdoms in the Tarim Basin and further areas which had been unknown to the Chinese before then. These accounts may have influenced the Han dynasty's later decision to expand westwards.
In 134 or 133 BCE, Emperor Wu launched an attack against the Xiongnu in the Battle of Mayi, and the centuries-long Han-Xiongnu Wars began in a few years later in 129 BCE. In the Battle of Hexi [zh] in 121 BCE, Han general Huo Qubing expelled the Xiongnu from the region, and four new commanderies were established on these lands, namely (from east to west) Wuwei, Zhangye, Jiuquan and Dunhuang.
From around 115-60 BCE, using the Hexi Corridor as a base of operations, the Han dynasty fought with the Xiongnu over control of the Tarim Basin. An important turning point in this conflict was the War of the Heavenly Horses, which allowed the Han dynasty access to the Ferghana horses, known as "heavenly horses" following Zhang Qian's account of them to the Han court. In 60 or 59 BCE, the Han dynasty gained control of the region and established the Protectorate of the Western Regions, partly because many of the oasis city-states in the Tarim Basin had become vassal states of the Han following the conquest of the Hexi Corridor and the War of the Heavenly Horses.
During the turbulent reign of Wang Mang, Han lost control over the Tarim Basin, which was reconquered by the Xiongnu in 63 CE and used as a base to invade the Hexi Corridor. Dou Gu defeated the Xiongnu again at the Battle of Yiwulu in 73 CE, evicting them from Turpan and chasing them as far as Lake Barkol before establishing a garrison at Hami.
After the new Protector General of the Western Regions Chen Mu was killed in 75 CE by allies of the Xiongnu in Karasahr and Kucha, the garrison at Hami was withdrawn. At the Battle of the Altai Mountains in 89 CE, Dou Xian defeated the Northern Chanyu, who retreated into the Altai Mountains. The Han forces, allied with the subjugated Southern Xiongnu, again defeated the Northern Chanyu twice in 90 CE and 91 CE, forcing him to flee west into Wusun and Kangju territories.

### Tang dynasty

The Tang dynasty fought the Tibetan Empire for control of areas in Inner and Central Asia. There was a long string of conflicts with Tibet over territories in the Tarim Basin between 670 and 692.
In 763 the Tibetans even captured the Tang capital of Chang'an for fifteen days during the An Lushan Rebellion. It was during this rebellion that the Tang withdrew its western garrisons stationed in what is now Gansu and Qinghai, which the Tibetans then occupied along with the area that is modern Xinjiang. Hostilities between the Tang and Tibet continued until they signed a formal peace treaty in 821. The terms of this treaty, including fixed borders between the two countries, are recorded in a bilingual inscription on a stone pillar outside the Jokhang in Lhasa.

### Western Xia dynasty

The Western Xia dynasty was established in the 11th century by the Tangut people. Western Xia controlled from 1038 CE up to 1227 CE the areas in what are now the northwestern Chinese provinces of Gansu, Shaanxi, and Ningxia.

### Yuan dynasty

Genghis Khan began the conquest of the Jin dynasty around 1207 and Ögedei Khan continued it after his death in 1227. The Jurchen-led Jin dynasty fell in 1234 CE with help from the Han-ruled Southern Song dynasty.
Ögedei also conquered the Western Xia dynasty in 1227, pacifying the Hexi Corridor region, which was later absorbed into the Yuan dynasty.

## Geography and climate

The Hexi Corridor is a long, narrow passage stretching for some 1,000 kilometres (620 mi) from the steep Wushaolin hillside near the modern city of Lanzhou to the Jade Gate at the border of Gansu and Xinjiang. There are many fertile oases along the path, watered by rivers flowing from the Qilian Mountains, such as the Shiyang, Jinchuan, Ejin (Heihe), and Shule Rivers.
A strikingly inhospitable environment surrounds this chain of oases: the snow-capped Qilian Mountains (the so-called "southern mountains" or "Nanshan") to the south; the Beishan ("northern mountains") mountainous area, the Alashan Plateau, and the vast expanse of the Gobi desert to the north.
Geologically, the Hexi Corridor belongs to a Cenozoic foreland basin system on the northeast margin of the Tibetan Plateau.
The ancient trackway formerly passed through Haidong, Xining and the environs of Juyan Lake, serving an effective area of about 215,000 km$^2$ (83,000 sq mi). It was an area where mountain and desert limited caravan traffic to a narrow trackway, where relatively small fortifications could control passing traffic.
There are several major cities along the Hexi Corridor. In western Gansu Province is Dunhuang (Shazhou), then Yumen, then Jiayuguan, then Jiuquan (Suzhou), then Zhangye (Ganzhou) in the center, then Jinchang, then Wuwei (Liangzhou) and finally Lanzhou in the southeast. In the past, Dunhuang was part of the area known as the Western Regions. South of Gansu Province, in the middle just over the provincial boundary, lies the city of Xining, the capital of Qinghai Province. Xining used to be the chief commercial hub of the Hexi Corridor.
The Jiayuguan fort guards the western entrance to China. It is located in Jiayuguan pass at the narrowest point of the Hexi Corridor, some 6 kilometres (3.7 mi) southwest of the city of Jiayuguan. The Jiayuguan fort is the first fortification of Great Wall of China in the west.