An imperial seal used by Emperor Kangxi will be up for auction at Sotheby’s next month, with the estimated grand starting price of US$15 million.

The Seal of the Mandate of Heaven is the largest and most powerful ever carved for the Kangxi Emperor, who himself was the greatest and longest-reigning monarch of China.

Carved for Emperor Kangxi, who ruled from 1661 to 1722, the seal bears the inscription “Jingtian Qinmin,” or: “respect heaven and diligently serve the people.” This phrase attests to the ancient Chinese philosophy that heaven grants authority to an emperor if he serves his people virtuously.

“Heaven’s will is the people’s will, so you have to respect your subjects to respect heaven,” said Nicolas Chow, Sotheby’s deputy chairman of Asia. “It’s a principle that still reminds everyone that the state ideology throughout most of Chinese history is Confucianism. It centers around the idea of benevolence and righteousness.”

Chow said Sotheby’s had auctioned a few imperial seals made of jade before, but none of them comparable to Kangxi’s in terms of size, material and historical importance. Unlike Chinese porcelain, which has a long auction record, imperial seals have only started getting much attention in the past decade.

Besides the seal, Sotheby’s will include two other objects in a joint auction. The first is a smaller seal of Kangxi made from soapstone. The second is one of only two copies of a catalogue recording 119 of Kangxi’s seals, the other copy of which is stored in Beijing’s Palace Museum.

According to Chow, all three objects come from different private collectors.