After two years of research, archaeologists Friday confirmed astronomical engravings had been found on a 2,000-year-old rock carving in North China's Inner Mongolia autonomous region.

The five holes spanning a distance of 1,000 meters were found in moorstone rocks in Yinshan Mountains in the regional capital Hohhot, said Wu Jiacai, archaeologist with Inner Mongolia Normal University.

Yinshan Mountains are famous for a large cluster of ancient rock paintings, and the carvings were found when archaeologists surveyed the area in 2015.

The 2-to-7-cm-deep holes, with diameters between 6 and 10 cm, form a string similar to a pearl necklace.

"When realized the holes were manmade, we began to investigate their meanings," Wu recalled. Archeologists used micro-erosion, a dating analysis technique, to confirm the holes were made during the late Warring States Period (475-221 B.C.) and discovered they represented Venus, Jupiter, Mercury, Mars and Saturn.

The formation of the five holes, for example, the curve formed and the distances between them, resembled the estimated position of the five planets in 204 B.C., archaeologists deducted. The rocks used were also different in color and texture.

For example, "Mars" was carved on a red rock, while "Mercury" was located near a creek.

"The carving was in fact an astronomical recording by our ancestors," said Wu.

Historical information suggests Modu, leader of the Xiongnu, defeated his enemies in 204 B.C., and the planets were likely to have been carved that spring at the foot of the mountain where he prayed, according to Wu.

The Xiongnu were a nomadic tribe which occupied a vast territory located in and around today's Mongolia and north China.

They founded their first empire in the third Century B.C. and were eventually conquered during the Han Dynasty (206 B.C.-220 A.D.).

"The carving not only shows the positional information of the five planets but also reveals characteristics of each, which will help us study ancient astronomic understanding," said Wu.