Luoyang Bridge (洛阳桥, Luòyáng Qiáo) is the oldest surviving stone sea-crossing bridge in China and one of the most audacious pieces of medieval engineering anywhere. Built from 1053 to 1059 under Song-dynasty governor Cai Xiang, it originally ran 1,200 metres across the Luoyang Estuary on the northeast edge of Quanzhou; 834 metres of the original stone structure still stand and are walkable.
What makes it historically extraordinary: to anchor the pilings in shifting tidal mud, the builders cultivated oyster colonies on the stones — the shells cementing the piers in place. It's one of the first recorded uses of bioengineering in civil construction, and walking beneath the bridge at low tide you can still see oyster-shell encrustation from nearly a thousand years of tidal cycles.
The bridge is one of the 22 UNESCO World Heritage sites of Quanzhou. A small on-site museum explains the construction; old stone tablets at both ends list the builder-donors from 1059. The bridge connects directly to Caixiang Ancestral Hall on the west bank (the Song governor whose vision this was), and a short walk south leads into Luojiang District's old street.
Practical: free admission. Best at low tide (check a tide table) for the oyster evidence. DiDi from Quanzhou old town: 20 min each way. Combine with Xunpu Village (both on the north-eastern side) as a day.