On the road to Spiti Valley there are many bridges now crossing the might Sutlej river.

The Tibet highway connecting this area with Tibet was cut into the mountain side on the right bank of the Sutlej and was once the only route. At that time bridge building was not possible over this kind of terrain.

Parts of the old highway can still be seen high above the new road, now much lower down. Bridges were built to cross over the river at various places where the valley was just too difficult to cut a road into that bank.

These bridges sometimes sometimes get washed away by flash flooding, the result of glaciers retreating in China and India, causing a deluge of water that destroys many bridges.

In this picture you can see why the bridge was needed. The left river bank (on the right here) is just too difficult while the other bank has more space to build the road.