The covered bridges are in fact a relic of the town wall dating from the 14th century. They are covering a part of Ill river in the city centre. In the past, the town gate was aditionally closed by a fencing gate. The four bridges made of wood were rebuilt of stone during the 19th century. One can also see four tours which served as prisons and reinforcement until 1832, and we still see the embrasures.
Place Henri Dunant, La Petite France, Strasbourg
Image source: ignis, wikimedia commons