A subway line under construction has traversed the ancient city of Xi'an, capital of northwest China's Shannxi Province, local officials said Tuesday.

The city's first subway line, the No.2 metro line, runs south-to-north underground two 600-year-old sites, the Ancient City Wall and the Bell Tower, said Xiang De, deputy director of the Shannxi Provincial Administration of Cultural Heritage.

"So far, settlement of earth works is far below our expectation," Xiang said. "We carried out a detailed safety assessment before construction to minimize hazards to cultural relics."

About 26 million yuan (US$3.8 million) have been invested for the protection of cultural relics during construction, said Luo Jifeng, chief engineer of the Xi'an Subway Co. Ltd.

The No.2 metro line began construction in 2007, and was expected to be completed in 2011, Xiang said. "It will improve the city's transportation markedly and promote its economic and social development."

Along the subway line are 57 historic sites. Since 2005, archaeologists have excavated 130 ancient tombs containing more than 200 cultural relics, Xiang said.

Xi'an's history stretches back more than 3,000 years and was once the capital of 13 dynasties of ancient China.

Six subway lines with a length of 251 km are scheduled to be built in Xi'an by 2020, among which the No.1, 2, 4 and 6 metro lines will be underneath the ancient city.

Famous historic sites along the six lines include the ruins of Chang'an City of the Han dynasty and the ruins of the Daming Palace of the Tang dynasty, Xiang said.

(Xinhua News Agency September 30, 2009)