The long Trans-Iranian Railway from Bandar Shah (now Bandar Torkaman) on the Caspian Sea to Bandar Shahpur (now Bandar-e Emam Khomeyni) on the Persian Gulf was opened during the reign of Reza Shah Pahlavi in 1939. The railroad was built with rail weighing and required more than 3000 bridges. There were 126 tunnels in the Zagros mountains, the longest of which was . Grades averaged 1.5 percent south of Tehran, but then increased to 2.8 percent to cross the pass between Tehran and the Caspian Sea.