Two abandoned cities lie within an hour of each other in the Turpan Basin of northwestern China, and between them they explain most of what made the Silk Road work. Jiaohe sits on a leaf-shaped island of loess between two river gorges. Gaochang spreads across the open desert plain about 40 kilometers to the east. Both were thriving, cosmopolitan trading towns for well over a thousand years, and both were left to the wind by the end of the fourteenth century. What remains is a landscape of earthen walls, stupas, and street grids so legible that UNESCO inscribed the two sites as components of the Silk Roads corridor in 2014.
This article looks at what each site actually is, how a desert basin was engineered to produce water in the first place, and why two of the wealthiest cities on the ancient route were simply walked away from.
Why the Turpan Basin Could Support Cities at All
Turpan is one of the strangest inhabited places on earth. The basin sits in a hollow between the Bogda range to the north and the Kuruktag hills to the south, and its floor drops to the Ayding Lake bed at 154 meters below sea level. That is the lowest land point in China and, after the Dead Sea, the second-lowest depression on the planet. Summer temperatures here have been recorded at 49.6 degrees Celsius. Annual rainfall averages about 16 millimeters, while more than 3,000 millimeters of water evaporates from the same ground in a year.
Nothing about that arithmetic favors farming. And yet Turpan has grown grapes, melons, and cotton for two thousand years, and it managed it because of water that never sees the sun until it arrives. Snowmelt from the Bogda and Kalawucheng mountains sinks into the gravel fans at the foot of the ranges and travels on underground as a slow, cold current. The people of the basin learned to intercept that current and lead it, still buried, out to the fields.
The result was an oasis economy. Water made the fields, the fields fed the caravans, and the caravans paid for the walls. Jiaohe and Gaochang are what that economy looked like once it had money.
Jiaohe: The City on a River Island
Jiaohe takes its name from its geography. The two characters mean intersecting rivers: two branches of the Yarnaz valley flow around a long plateau and meet again on the far side. The city was built on top of that island, about 10 kilometers west of modern Turpan, on a strip of land roughly 1,650 meters long and never much more than 300 meters wide, standing some 30 meters above the water.
A fortress you could not surround
The site reads as a natural citadel, and that is precisely why it was chosen. Steep cliffs on every side made an approach impossible except through controlled gates, and the rivers guaranteed a water supply that could not be cut off by a besieging army.
Chinese heritage authorities describe Jiaohe as the largest, oldest, and best-preserved earthen-architecture city in the world, and as the most complete surviving urban site in China. The claim rests on an unusual fact: almost nothing here was ever built of stone or fired brick. The walls, streets, houses, and temples were all cut and compacted out of the same loess plateau they stand on.
That method is also why the site is so readable today. Builders excavated courtyards downward into the ground rather than stacking walls upward, so the city is essentially a network of sunken rooms, corridors, and cellars carved out of the earth. When the buildings fell out of use, the hollows stayed behind.
What the streets still show
Walk the site and the planning is immediately obvious. The city is divided into five functional zones: a residential quarter, storage areas, the government offices, a temple district, and a cemetery beyond the walls. A central avenue runs along the spine of the plateau, with lanes branching off it at right angles — a grid that will look familiar to anyone who has visited a Chinese city, because it descends from the same urban tradition.
The sequence of occupation explains the layout. Jiaohe was already a settlement in the second century BCE and served as the capital of the Jushi, one of the thirty-six city-states recorded in the Western Regions. Its street plan was laid out under the Qu family rulers of Gaochang in the fifth to seventh centuries, took its surviving shape under the Tang in the seventh and eighth, and was inherited by the Uyghur kingdom that followed from the ninth through the thirteenth.
In 640 CE the Tang court established the Anxi Protectorate here — the highest military and administrative office the empire maintained in the Western Regions. For a period, the most powerful Chinese official west of the Gansu corridor worked from a building on this river island.
A cemetery that rewrote the story
Excavations in the burial grounds on the northern terrace produced one of the most useful finds at the site: the tombs of Jushi nobles, stocked with objects that trace the reach of the trade passing below. Archaeologists have catalogued Chinese silk and lacquerware, imitation cowrie shells and Han-era wuzhu coins, a wooden box carved with cloud scrolls, silver ornaments in the shape of water buffalo, and gold plaques showing a tiger and an eagle locked in combat — a design associated with the steppe cultures to the north. A single grave can hold goods from three different worlds, which is a compact way of saying what the Silk Road was.
Gaochang: The Western Regions' Chang'an
Gaochang is larger, flatter, and more obviously a capital. It covers about 198 hectares on the plain roughly 40 kilometers east of Turpan, at the point where the Mutougou stream leaves the Flaming Mountains — the red ridge that appears in the classic novel Journey to the West. The outer wall runs about 5.44 kilometers around and still stands in long, solid stretches, so the shape of the city is easy to read from ground level: an irregular square containing an outer city, an inner city, and a palace enclosure at the center.
Travelers who know Tang-dynasty Chang'an, or have seen its surviving plans, tend to notice the resemblance at once. Gaochang was laid out on the same principle of nested rectangles and axial streets, which is why it is often called the Chang'an of the Western Regions.
From garrison to kingdom
The city began as a Han frontier post in the first century BCE, growing from a walled garrison into the seat of a commandery. In 327 CE the Former Liang state established Gaochang Commandery here, the first application of the Chinese commandery-and-county system in the Western Regions. From 442 to 640 it was the capital of the Gaochang Kingdom, ruled for its final century and a half by the Qu family. The Tang then took the city, renamed the region Xizhou, and administered it as a prefecture until the end of the eighth century. From the middle of the ninth century it served as the capital of the Uyghur kingdom of Gaochang, which submitted to Genghis Khan in 1209. In one form or another, the city was in use for close to 1,400 years.
The Xuanzang connection
Gaochang's most famous encounter took place in 627 CE, when the monk Xuanzang passed through on his way to India. The Gaochang king, Qu Wentai, was a devout Buddhist who had heard the traveler was approaching and sent an escort to bring him in. He then did everything he could to keep him. According to the biography of Xuanzang compiled by his disciple Huili, the king offered him a permanent post as the kingdom's chief religious teacher. When Xuanzang refused, Qu Wentai threatened to send him back to China, and Xuanzang answered by refusing food until the king gave way.
The compromise became one of the more human stories in Silk Road history. The two men swore brotherhood before a Buddha image. Qu Wentai then equipped the journey at state expense — robes, gold and silver, bolts of silk, horses, and attendants — and, most usefully of all, wrote twenty-four letters of introduction, one for each kingdom Xuanzang would cross, each accompanied by a bolt of fine silk as a credential. Xuanzang promised to come back and stay three years on his return. He kept the promise but arrived too late: by the time he came home from India, the Tang had annexed Gaochang and Qu Wentai was dead.
What survives
Three structures are usually pointed out to visitors: the small temple in the southeast, the great temple in the southwest, and the fortified compound in the middle of the site known as the Khan's Fort. The southwestern temple is the one linked to the Xuanzang story, since tradition places his lectures there. Beyond these, most of what you see is wall — rammed earth and sun-dried brick, eroded into fin-shaped buttresses by six hundred years of wind.
The Karez: Moving Water Without Losing It
None of this would exist without the karez, the underground irrigation system that makes agriculture possible in the basin. A karez is not simply a canal and not simply a well. It is a chain of both, made up of four parts: vertical shafts, a gently sloping underground tunnel, a surface channel, and a storage pond.
How the system works
The logic is entirely about evaporation. Dig an open canal across the Turpan Basin, and the sun will take most of the water before it reaches a field. So instead, a karez taps the underground current where the gravel fan meets the plain, then carries it through a tunnel cut at a very slight downward angle — enough to keep the water moving, not enough to expose it. Vertical shafts spaced along the route let workers haul out spoil during construction and descend for maintenance afterward. From above, the shafts read as a long line of circular spoil mounds across the desert, which is how you spot a karez from a car window before you know what you are looking at.
Only at the far end does the water come to the surface, into an open channel and then a pond that regulates the flow before it reaches the fields. Because virtually the whole distance is underground, the system loses very little to sun or wind, and it keeps delivering when surface channels have run dry.
How old is it, exactly
This is one point where the popular account and the technical one diverge, and it is worth being precise. Turpan's karez are commonly described as more than two thousand years old, and the idea behind the system is certainly ancient. But radiocarbon dating of surviving channels, read together with the documentary record, points to the fifteenth century for the earliest karez now in evidence, with steady expansion in the nineteenth century and a boom from the mid-nineteenth century into the 1960s. Similar systems were built in Persia, where they are called qanats, and the technology traveled along the trade routes in both directions.
The scale is what impresses. Turpan city officials counted 977 surviving karez in 2023, of which 214 still carried water, adding up to roughly 3,492 kilometers of tunnel. At the system's historical peak in the late eighteenth century, the karez of the region are recorded as extending over 5,000 kilometers, with more than 1,200 kilometers of that inside the Turpan Basin alone. China's cultural heritage administration added the karez to the national protection list in 2006, and in 2024 the system was named a Chinese candidate for recognition as a World Heritage Irrigation Structure.
One of China's three great ancient works
The karez is routinely grouped with two far more famous projects. Chinese cultural authorities and reference works commonly describe it, alongside the Great Wall and the Grand Canal, as one of the three great engineering works of ancient China. The comparison says less about size than about ambition. On that list, one project was built to keep people out, one to move grain, and one to move water without losing it to the desert.
Why Both Cities Were Abandoned
Neither city fell in a single catastrophe. Jiaohe's decline followed the shifting of trade routes and of the region's political center. After the Mongol conquests and the reordering of Central Asian commerce, the island city lost its reason to exist and was given up toward the end of the fourteenth century. Gaochang, the more important of the two for most of its life, was destroyed in the wars that followed the collapse of Uyghur power in the region and was abandoned in the same period.
The water, notably, did not fail. The karez kept running. What disappeared was the traffic — the caravans, the tax revenue, and the political weight that had paid for the walls in the first place. The two cities are a reminder that Silk Road prosperity was never a permanent property of a place. It was a function of routes, and routes can move.
Visiting Jiaohe and Gaochang Today
- Jiaohe lies about 10 kilometers west of Turpan on the road toward the Yarnaz valley. Allow two hours to walk the main axis and the temple district properly.
- Gaochang is about 40 kilometers east of the city and is usually combined with the Bezeklik Thousand Buddha Caves in the same valley.
- Go early or go late. The basin is brutally hot from June through August, and the first two hours after opening and the last two before closing are the only comfortable windows in summer.
- Bring water and a hat. There is almost no shade on either site, and the ground radiates heat well into the afternoon.
- September and October are the best months, coinciding with the grape harvest, when the drying houses and markets around Turpan are at their busiest.
- Wear shoes with grip. You are walking on compacted earth and loose gravel, and some paths run close to the edge of the cliffs.
Frequently Asked Questions
Are Jiaohe and Gaochang UNESCO World Heritage Sites?
Yes. Both were inscribed in 2014 as components of the Silk Roads: the Routes Network of Chang'an-Tianshan Corridor, a transnational listing jointly nominated by China, Kazakhstan, and Kyrgyzstan. The corridor covers 33 sites across the three countries, 22 of them in China, and Jiaohe and Gaochang belong to the group of six component sites in Xinjiang.
What is the difference between Jiaohe and Gaochang?
Jiaohe is the smaller, older, and more dramatically sited of the two: a compact city on an island plateau between two river gorges, with its buildings cut down into the earth. Gaochang is far larger, spread across the open plain, walled on a roughly square plan, and for most of its history the more politically important of the two.
Which one should I visit if I only have time for one?
Jiaohe, if the choice is forced. The setting is extraordinary, the layout is easier to read on foot, and it is closer to Turpan city. Gaochang rewards anyone with a particular interest in Tang urban planning or in the Xuanzang story, and it is normally paired with the Bezeklik caves.
Is the karez still in use?
Partly. Of roughly a thousand surviving karez around Turpan, a few hundred still carry water and continue to irrigate fields and vineyards. The system declined through the twentieth century as motorized pumps lowered the water table, and local authorities have since run programs to close illegal wells, clear and repair channels, and keep the remaining karez flowing.
How old is the karez system?
Older than the documentary record can settle. Popular accounts date it back more than two thousand years, but radiocarbon dating and written sources point to the fifteenth century for the channels that survive today, with major expansion in the nineteenth and twentieth centuries.
Where These Facts Come From
Figures in this article are drawn from official and institutional sources rather than secondary travel writing. The main ones:
- China's National Cultural Heritage Administration, on the 2014 Silk Roads inscription, the 33 component sites across three countries, and the national protection listing of the karez in 2006.
- The Turpan municipal government and the Gaochang district government, on the dimensions, construction phases, and city plans of both sites.
- China Daily and Xinhua reporting, on the description of Jiaohe as the largest and best-preserved earthen-architecture city in the world.
- China Water News and the Xinjiang karez research association, on the 2023 count of 977 surviving karez and 214 flowing channels.
- The biography of Xuanzang compiled by his disciple Huili, as cited in major Chinese media accounts of the Gaochang episode.
