The Qi wall was constructed more than 2,500 years ago.[Photo by Ju Chuanjiang/for China Daily]

It's an engineering feat from ancient times, but the wall constructed by the Qi State more than 2,500 years ago has been largely ignored. Zhao Ruixue chats to a man committed to exploring this slice of history.

Photographer Hu Deding, 63, never thought he would spend more than 10 years exploring an ancient engineering project seldom visited by tourists.

"I came across the ancient wall and found it so amazing. I just can't stop walking it and exploring it again and again," Hu says.

The wall Hu has been visiting was built by the Qi State in the Spring and Autumn Period (770-476 BC) and the Warring States Period (475-221 BC).

Investigations have shown that the Qi wall stretches across East China's Shandong province for 620 kilometers, from Jinan on the bank of the Yellow River to the coastal city of Qingdao in the east.

"When mentioning the long wall, people tend to think about the Great Wall built in the Qin Dynasty (221-206 BC) and in the Ming Dynasty (1368-1644). In my opinion, the Qi wall is no less important than the Great Wall of the Qin and Ming dynasties," Hu says.

Gary Feinman, curator of anthropology at the Field Museum in the United States, walked the easternmost 50 kilometers of the Qi wall.

"The Qi wall is a very important and impressive historical feature that miraculously still is visible across Shandong's landscape almost 2,500 years after it was built," Feinman says.

According to Fang Hui, head of the Institute of Cultural Heritage under Shandong University, the Qi wall is more than 300 years older than the more famous Great Wall first constructed by Emperor Qin Shihuang (260-210 BC).

Qin Shihuang, the first emperor of the Qin Dynasty, started building the Great Wall more than 2,000 years ago, which has become the world's largest man-made structure after it was expanded in the following dynasties. According to survey results released by the State Administration of Cultural Heritage in 2012, the Great Wall measures 21,196.18 kilometers in total.