The Trans-Persian Railway Opening

 At one point, it zigzags three times up the side of a mountain. Another challenge was the construction of a bridge across a narrow valley to allow the train to exit a tunnel from the side of one mountain and enter another tunnel on the side of an adjacent mountain. In order to build the arch of the bridge 70 metres above the river valley, the builders had to erect two iron platforms supported by slats or meshes of fortified concrete.