The rest of the buried treasures, mostly from tombs of some illustrious families of ancient Beijing, will remain in peace in their original state.

Among the unearthed treasures are bronze mirrors, earthenware pots, snuff bottles, porcelain jars and a large collection of jewels such as earrings, hairpins, rings, bracelets, mostly made of gold, silver, pearl beads, amber and amethyst. Some are from the Han Dynasty of 2,000 years ago.

According to Song Dachuan, head of the Beijing Historical Relics Institute, the most precious discovery was 10 jade belts found in a cluster of 179 tombs for eunuchs near the Olympic shooting venue in the western part of Beijing, which used to be the burial place for royal and noble families. Most of the jade belts bear intricate carvings of floral and dragon patterns.

"And most surprisingly, two of the jade belts were made of glass and they can help researchers learn about China's glass making technology," Song added.

"We found many exquisite artifacts with considerable historical value in the eunuchs' tombs," Song said.

The remains of the excavated tombs are also providing insights into the burial customs of ancient Beijing.

For example, mortar and bricks tombs were usually for poor people and jars made of blue and white porcelain were commonly used to carry the remains of monks.

Although most of the tombs found in the northern part of Beijing, near the sites of the Olympic Village and the futuristic Bird's Nest and Water Cube, were civilian tombs, the discovery will also help archaeologists conclude for the first time that no city was built in the north of present Beijing.

The two-and-half years' archaeological research also gives them a chance to get first-hand information to prove that the most ancient city built on this piece of land could date back more than 2,000 years, in the Han Dynasty (206 BC - AD 220).

"Apart from these archaeological discoveries, we got a chance to preserve and renovate some crumbling ancient structures, as some of them were used as shelters and storage areas for civilians a few decades ago when the government did not pay attention to the protection of cultural relics," Kong said.