The Trans-Iranian Railway was a major railway building project started in the 1930's and finished in 1939, under the direction of the Persian monarch, Reza Shah, to construct a basic network of railways joining the capital Tehran to the Persian Gulf and Caspian Sea. The Trans-Iranian Railway was built entirely by local capital.

The first lines pass though formidable mountains, and international construction firms where heavily involved in the construction. Gradients up to 1 in 36 were required, plus hillclimbing techniques such as spirals were required. All sorts of geological problems were encountered, which required abandonment of some tunnels, and realignment of the route through different terrain.

The principle lines were completed ahead of schedule and under budget, with the first train arriving in Tehran in about 1940.