NANJING, Jan. 11 -- The site of Changgan ancient city, unearthed in Xijie site of east China's Nanjing City, has been confirmed to date back to 3,100 years ago, extending Nanjing's history by more than 600 years, Nanjing institute of archaeology said Wednesday.

The site of the ancient city, named "Changgan," the earliest known name of the city of Nanjing, features relics of a platform, ring ditches, walls, doorways and sacrificial pits.

During excavations that began in 2017, archaeologists unearthed four ring ditches from the Shang and Zhou dynasties (1600 BC-256 BC), containing collapsed rammed-earth walls, said Chen Dahai, an archaeologist with the institute, responsible for the excavation.

"We also found more evidence supporting our conclusion, including a well on the side of the ditch that was originally constructed during the late Shang Dynasty and the unearthed pottery featuring triangular and ladder-pattern decorations with clear characteristics of the Shang Dynasty," Chen added.

Various artifacts, including pig bones and charcoal, date back to the period ranging from the late Shang Dynasty to the early Zhou Dynasty, according to carbon-14 dating data, Chen said.

Up to now, the excavation area at the Xijie site has reached 12,000 square meters, with more than 500 relics of various types and over 10,000 specimens of archaeological importance unearthed.