Cast-iron evidence

Unlike porcelain, which is widely seen as a staple of ancient China's maritime trade, discovery of over 130 metric tonnes of iron from Nanhai One probably surprised the general public. However, for professional researchers like Shen Ruiwen, an archaeology professor at Peking University, it was not surprising at all－it just provides evidence of the prosperous iron trade, as recorded in historical documents.

For example, in Brief Introduction to Foreign Islands, a book compiled by a Yuan Dynasty navigator in 1349, iron made in China, including "ironware", "iron pots", "iron bars" and "iron lumps", among other forms of the black metal, were exported to 48 countries and regions aboard merchant ships setting off from Quanzhou.

"Iron was a key commodity in China's export along the maritime Silk Road during the Song Dynasty," Shen says. "Analysis of the findings on Nanhai One indicates the iron came from Fujian, but where exactly it was produced still awaits follow-up research."

A newly excavated archaeological site in Anxi county, Quanzhou, may shed light on it, though. The Xiacaopu iron production site in Qingyang village, also part of the newly inscribed World Heritage property, has provided crucial physical material to help understand the iron and steel-making technology of the Song-Yuan period.

Since 2019, archaeological excavation led by Shen discovered six smelting furnaces, a group of ancient mining pits and a segment of an ancient trail, among other remains, within an area of 50,000 square meters.