Ancient residences are excavated in Sichuan province. [Photo provided to China Daily]

Archaeologists have discovered more than 3,500 ancient post holes on the Anning River Plain in Sichuan province.

The holes were made to hold posts for the construction of shelters more than 1,800 years before the establishment of the Qin Dynasty (221-206 BC), China's first feudal dynasty.

The holes were found in 2014 after archaeologists began the excavation to ensure no cultural relics were damaged in the building of the Emei-Miyi section of the high-speed Chengdu-Kunming railway line linking Sichuan and neighboring Yunnan province, said Song Ming, an information officer with the Liangshan Yi autonomous prefecture government.

Chen Wei, a leading archaeologist from the Sichuan Provincial Cultural Relics and Archaeology Research Institute, said archaeologists from the institute as well as the Liangshan Yi Autonomous Prefecture Museum and Panzhihua Bureau of Cultural Heritage cooperated in the excavation.

Nearly 50 square pits dating back to the pre-Qin period were found, with the length of their sides ranging from 2.8 to 3.5 meters, and depths ranging from 0.15 to 0.6 meters. They could be the remains of semi-crypt type residences, Chen said.

It was the largest number of remains of semi-crypt type residences ever found on the Anning River Plain, he said.

Graveyards covering more than 2,000 square meters were discovered in the excavation. Most of the tombs were made of vertical pits, urns and stones.

Archaeologists hailed the findings on the Anning River Plain in Liangshan and neighboring Panzhihua as the second-largest number of pre-Qin human settlements ever found in Sichuan, behind only those on the Chengdu Plain.

"They will also change the long-standing concept that Liangshan was barren in ancient times," Song said.