Inscriptions on bricks on the imperial Ming Dynasty (1368-1644) Great Wall section are fading owing to wind and rain erosion for centuries and deterioration of the environment in recent years.
The inscribed bricks are mainly found on the sector of the Great Wall sections in north China's Hebei province, according to Hao Sanjin, a member of the Great Wall Society of China.
The characters mainly record data about the soldiers who built and guarded this section of the wall.
So far, 16 such records have been discovered.
The existing bricks span several reign periods of Ming emperors, noted Hao, while a few date from the period of Northern Qi State (550-577), the earliest discovered so far.
"It is generally recognized that the inscribed bricks provide valuable historical clues for the study on the construction of the Great Wall and the military history of the border area at that time," said Hao.
Characters have peeled off dilapidated bricks on the Great Wall sector at the Shanhai Pass, the last section of the Ming wall to be built.
According to a worker at the Shanhai Pass cultural relics preservation office, in the 1980s those characters were still distinct and easily decipherable.
Archaeologists are calling for a survey of the surviving inscribed bricks as soon as possible.