Unearthed tiles helped archaeologists to confirm its age — around the time when the Qin state conquered other rival states and united China. Bricks, ceramic pipes, and other structural components were also discovered, enriching experts' understanding of the structure.

"An architectural complex of such a large scale and unique layout has rarely been seen in previous archaeological findings," Hou said. "It would have been a key ceremonial structure during the time of Qin empire. It marks a united country with a centralized power."

The area that is present-day Lixian county witnessed the rise of the Qin state as a ruling power amid chaotic conflicts among numerous vassal states during the Spring and Autumn (770-476 BC) and Warring States (475-221 BC) periods. Before the political center of the Qin state was moved eastward to present-day Shaanxi province, the eastern part of Gansu province was where generations of its rulers lived.

In the 1990s, the stunning discovery of Lixian's Dabuzishan site, a complex of Qin-state mausoleums, offered even greater insight into the history. The gold decorative fillets unearthed from the site became the signature artifacts that demonstrated the wealth and social prosperity of the Qin Dynasty.

A key, nationwide academic project was launched in 2004 to decode early-stage Qin culture and its relation with nomadic ethnic groups to the west through archaeological studies. Including Dabuzishan and Sijiaoping, the sites in Lixian have become pivotal to the project.

"The early national-level sacrificial ceremonies are a crucial part of our studies," Hou said.