The Prince Kung's Palace Museum has more than 50 tribute bricks bearing the inscriptions indicating the names of ancient craftsmen and plants in Linqing, says Sun Dongning, deputy director of the museum's academic committee.

It reflected the production norms of Linqing tribute bricks, where responsibility was assigned to individuals, Sun explains.

Sun says that 90 percent of the bricks used in the buildings along Beijing's Central Axis are tribute bricks from Linqing, especially the wall bricks, making them an important cultural element.

Architects, generations ago, put a premium on Linqing brick for its superior quality, delightful color and malleability.

"The bricks can be molded into a variety of shapes and sizes. Thus, they are highly versatile for different construction needs," Zhao says. "They are also resistant to corrosion."

The local chronicle also recounted the bustling brick production scenes, where official kilns in Linqing were distributed in large numbers along the banks of the Grand Canal.

"The soil in Linqing, commonly known as 'lotus soil', is excellent, fine and free of impurities. Bricks made from this soil are exceptionally hard and produce a pleasant metallic sound when struck, making them ideal building material," Zhao says.

The "lotus soil" features layers of red, white, and yellow clay buried a meter deep in many places of Linqing and is a result of frequent floods from the Yellow River.

Additionally, the water in Linqing is clear and slightly alkaline, suitable for brickmaking, he adds.

The ideal production conditions and easy transportation via the canal are reasons behind the widespread presence of the bricks in Beijing, he explains.

As the country has stepped up efforts in protection and restoration of cultural relics, especially ancient buildings, tribute bricks have been in demand.