"Xian is an ancient city. Yet at the same time it is a young city," said Han Ji, deputy chief of the Municipal Planning Bureau here. The capital of 12 dynasties, including the glorious Han and Tang empires, Xian combines ancient monuments such as the great Goose Temple and the Grand Mosque with bustling modern industry and a galaxy of scientific and educational institutions.
How to preserve the old, while giving enough breathing space to the new, is the problem that faces Mr. Han and his colleagues in the city's planning and environmental bureaus.
In the outskirts of Xian is the world-famous tomb of the first Qin emperor, guarded by an army of 6,000 life-size terra cotta soldiers.
The First Emperor unified China, built the Great Wall, and decreed that his successors should bear the titles Second Emperor, Third Emperor, and so on throughout eternity. Within five years of his death, in 210 BC, his dynasty had been overthrown. It was followed by the more stable and much more long-lived Han dynasty.
Xian, known through most of its history as Chang-An (eternal peace), reached its height under the Tang Dynasty (AD 618-907). By then it counted a million inhabitants, living within walls extending six miles east to west and about five miles north to south.
Here the great poets Li Po (701-762) and Du Fu (712-770) spent part of their wandering lives. Here the handsome, brilliant Emperor Xuanzong (Hsuan-Tsung) fell in love with the Lady Yang, forgetting state cares to such an extent that he lost his empire and his love.
The hot springs resort where Xuanzong and his beautiful but plump mistress used to watch steam rise from the pool on cold February mornings till serves bathers, Chinese and foreign alike.
Chang-An, in Tang times, was unquestionably the greatest, most magnificent city on earth. No European town of those days, overrun by barbarians, could rival it. Unlike later eras, the capital of Tang was open to all races, religions, and influeces: Buddhism, Islam, Nestorian Christianity.
Merchants from Arabia and Byzanthium, Persia and Japan jostled in its wide, straight streets. The Great Mosque, an Islamic structure built entirely in Chinese style, with sweeping tile roofs supported by massive wooden pillars, dates from this period. People flocked to Chang-An from remote parts of the Eurasian continent and the islands beyond to stare, to buy, above all, to learn.
"I'm proud of our past," said a young worker in a machine tool factory who accosted a visitor to practice in English. "We invented gunpowder, and printing , and papermaking. Our art and our sculpture were the best in the world."
Today, he continued, he knew that China had fallen far behind the industrialized nations of the West.
"But we are willing to work hard," he said. "Come back in 20 years' time. I hope you will see some progress."
The Xian of today covers more ground than did the Chang-An of Tang days. But for many centuries it was just a small provincial capital. In 1949, when the People's Republic was established, it had only 390,000 people "and less than 2, 000 bicycles," said Mr. Han.
The city walls of Xian, built during the Ming Dynasty (1368-1644), enclosed an area of some five square miles -- one eighth the site of the Tang city. Still, Xian is one of the few cities of China to have kept its old walls, even though they are crumbling in parts.
Mr. Han has an ambitious plan to restore the walls, especially the four main gates -- north, south, east, west. The west gate was rebuilt last year and houses a small museum of Xian's past. The north gate is under restoration now.
Mr. Han is from Peking, where he was a student of the great architect Liang Shicheng. In the early days of the People's Republic, Professor Liang had a grandiose plan to preserve Peking's walls and gates, and to turn them into flowering walkways and cultural monuments.
But then Mao Tse-tung publicly dressed down the professor for thinking in such extravagant terms of the feudal past. Peking's walls and gates were demolished one by one. Many other cities of China followed suit, but not Xian.
"It was thanks to Xi Zhongxun, then deputy premier, that we could keep our walls," Mr. Han recalled. Mr. Xi, who hails from the Xian area, sided with those city fathers who wanted to preserve the walls as a monument to the past. Today, the area within the walls is the busiest, most animated section of the city, with bustling shops and marvelous tile-roofed courtyard gates leading to a maze of alleys.
"We intend to preserve this area as a commercial and residential section," said Mr. Han.
Industry is concentrated in the southern outskirts of the city, since the prevailing winds are from the northeast and will help to blow airborne pollution away. Factories now inside the city are being asked to move, but the process is slow and will take at least 20 years to complete, according to Mr. Han.
Present-day Xian covers about 45 square miles (old Chang-An had about 30) and has a population of 1.4 million.
There is a heavy emphasis on education. Shanghai's famed communications university, which specializes in science and technology, has set up a branch here.
Almost all the students I interviewed at one high school wanted to go to this university, many of them hoping to enter the difficult computer sciences department. Among the many other institutes is one that specializes in the history and archaeology of Han and Tang times.
In flat Xian, cars are still a rarity, but the age of the two- and three-bicycle family has arrived with a vengeance.
"We have 800,000 bicycles today, more than 1 for every 2 inhabitants," said Mr. Han. He didn't know how that compared with the number of oxcarts and palanquins in Tang times, but of one thing he was certain: "If you consider that the Han and Tang periods represented two peaks for Xian's glory, then I think we can safely say that we are enjoying our third peak today."