The experts, who have long been immersed in Dunhuang studies, reached the conclusion through studying captions, scriptures and other literary documents in the grottoes.

According to these experts, the three classes of people were the grotto owners, benefactors, including the investors and foremen, and craftsmen, such as brick-layers, carvers, painters and carpenters.

Mogao grotto owners were from various walks of life, including ranking government officials, eminent, esteemed monks, and tribal leaders, said the experts.

The time taken to build a grotto was decided by a number of factors, including the scale, financing and influence of the grotto owners, and social changes.

It took one to three years to dig a bigger grotto, a matter of several months to two years for a smaller one, while a grotto with sculptures tens of meters tall needed four to five years to complete, said the experts.

Fresco and sculpture painting took relatively a shorter period of time, normally three to six months, they said.

The Mogao Grottoes of Dunhuang, popularly renowned as the Thousand Buddha Caves, were carved out of the steep, rough rocks stretching about 1,600 meters (5,249 feet) along the eastern side of Mingsha Hill, 25 km (16 miles) southeast of Dunhuang. Construction began in 366 AD and continued for the ensuing 10 or so dynasties.

In the year 1900, a noted Taoist priest, Wang Yuanlu, discovered a cave at the site which contained more than 50,000 sutras, documents and paintings of nearly 10 dynasties ranging from the 4th to the 11th century.

The United Nations Educational, Scientific and Cultural Organization (UNESCO) listed the Mogao Grottoes on the World Heritage List in 1987.

(People's DailyJuly 31, 2002)