Archaeologists discovered widespread silt deposits beneath the foundations of the palace, along with traces of artificial clearing, confirming the initial guess that the palace was built on a drained lake, a phenomenon that had never been seen before at other palace sites of a similar date. To people's surprise, the silt deposits petered out a short distance to the north of the site, indicating that more suitable construction areas were available nearby. Why then was a lake bed — with all the complexities of construction — used instead of firmer ground?

"Historical records indicate that the Qin people revered the virtues of water. We guess they deliberately built the complex at the bottom of the drained lake. Looking back on the construction of Emperor Qinshihuang's mausoleum, we know it had a giant water control system, which means the mausoleum was also built somewhere rich in water. Maybe the emperor just preferred locations with abundant water resources, but that decision did significantly increase the earthworks for the palace's construction," says Liu.

Archaeologists further found that the complex seemed to have a north-south central axis, which evenly divided the whole Guanzhong Plain into two halves. The choice of the location may also be related to the emperor's wish to build the complex on the axis, Liu says.

Qin laborers might have drained the lake first, followed by treating the underlying silt to achieve a relatively uniform thickness. After this, foundation ramming was carried out in sections.

He Jiahuan, another member of the archaeological team, says they initially thought the rammed earth platform of the palace, which is about 1,270 meters long and 420 meters wide, was rammed as a single, uniform structure, but their studies suggest that the platform was rammed in sections.

"Vertically, the foundation was layered: the lower layer was rammed first, followed by the upper layer. Horizontally, it was constructed in sections. For example, the southern section was rammed first, followed by the northern section. Thus, the entire foundation was essentially built layer by layer and section by section through ramming," says He.

He says this approach allowed the quality of the construction work to be better controlled, but managing the construction was more demanding.