 Other examples of Song bridges include <unk> Bridge , a stone arch bridge in <unk> , Zhejiang Province . The bridge was built in 1213 , the sixth year of the <unk> Era in the Southern Song dynasty . Song @-@ era <unk> bridges include the <unk> Bridge , 400 m ( 1 ⁄ 4 mi ) long , which may still be seen today . 
