When Marco Polo visited the great fortress city of Heicheng (the Black City) in the Inner Mongolian Desert, it was a green and lovely place. The reason: water of the Etsin-Gol rushed down from the everlasting snows of the Qilian mountain range.
But today, Heicheng (or Etzina, as Marco Polo called it), is a bleak, sandswept ruin all but swallowed up by the encroaching Gobi Desert. Photographs of Heicheng and its massive walls rising starkly from a treeless wasteland are used by Chinese authorities to publicize the continuous fight man must wage against the desert if he is to wrest his living from the soil.
Here in Dunhuang, 525 kilometers southwest of Heicheng as the crow flies, the lesson of the ruined Black City is not lost. Dunhuang, one of four counties established by Emperor Wu of Han in the first century B.C., has been an important outpost of Chinese culture ever since. Tourists know Dunhuang as one of the key cities of the ancient silk road to Persia and Europe, and as the site of the world-famous Mogao Buddhist caves.
But to the people of Dunhuang, the problem is how to keep their oasis green and how to feed themselves when population has more then doubled in the last 30 years.
''In Tang times,'' said Zhang You-cai, manager of the Dunhuang Hotel, ''our population was 40,000. And when I was a young man, 30 years ago, it was also 40, 000. But today we have 95,000 people, and only 30 or 40 millimeters of rain per year.''
Fortunately there is ground water in Dunhuang, fed by the snows of the Qilian mountains and by a river from the same source. Dry part of the year, in August it can turn into a raging torrent.
The 10 communes of Dunhuang have built a common reservoir from which water is carefully apportioned to each by turn, running along an intricate system of canals.
This water helps communes like Yangjiaqiao (''bridge of the Yang family''), near the Mogao caves and on the edge of the Mingsha Shan (whispering sand) dunes , to seize land back from the desert.
Mingshan production brigade (village) is one of nine production brigades belonging to Yangjiaqiao commune.
''We have 923 people, tilling 2,000 mou (134 hectares),'' said Communist Party Secretary Zhang Fengshan when I visited his village recently. ''Nearly one third of this land is what we reclaimed from the desert ourselves.''
Secretary Wang is tall and big and speaks with a booming voice. If the desert is the enemy, Mingshan is on the front line of the struggle. The fields of this village end abruptly in sand. In some places they are even cradled by dunes more than 10 meters high.
''The key to our fight is water,'' said Secretary Wang, standing atop one recently stabilized dune, ''we can only reclaim five mou per year, whereas if we had enough water we could easily reclaim 200 mou (13.4 hectares) per year. We are limited in what we can do by the water that other communes are willing to let us have. Nevertheless, we are pushing back the desert year by year.
''This dune we're standing on is not going to move any more -- it's not going to pile up sand in our fields every time the wind blows -- and I can assure you that when it blows, it really blows. ''Why? Because we have planted rows of trees straight across the path of the blowing wind.
''White poplars and willows grow fast and provide much shade. Once the trees are grown -- white poplars take only three years -- the dune cannot move and we can start clearing land and planting crops. This sandy soil is fertile once you have proper irrigation and drainage. Look at that wheat over there -- it's growing quite nicely. And on the other side we have an orchard...''
It all sounds easy today. Yet Mr. Wang said his villagers experimented for 20 years until they found the best way to tackle the desert. In Dunhuang no progress was made until, with the advice of the Desert Research Institute of Lanzhou, the villagers planted trees to act as windbreaks.
''In the past half-century, desertified land has increased by 50,000 square kilometers,'' said Prof. Liu Shu, associate director of the Desert Research Institute. ''Altogether, 1,490,000 square kilometers, or 15.5 percent of all China's land, is arid, and of this 328,000 square kilometers, 3.4 percent, is desertified.''
The work in Dunhuang is part of an ambitious nationwide program to create a green belt stretching from Xinjiang (Sinkiang, or Chinese Turkestan) all the way across Inner Mongolia to the northeast (Manchuria). ''Eighty-five percent of desertification is caused by human factors - overcropping, overgrazing, and chopping trees for firewood in disregard of natural laws,'' Professor Liu said.
Dunhuang is an encouraging example of a reversal of this process. But to spread these examples throughout the country, she went on, a concerted effort must be made in many different areas, from tree-planting to rational crop-raising and grazing policies to population control. Only then will a Marco Polo of the 21st century return to find his lost city abloom again.