In 1845, Isambard Kingdom Brunel surveyed and prepared parliamentary plans for the Vale of Neath Railway which involved a 2,497-yard hole through the hill between Merthyr Tydfil and Aberdare, the second longest of Wales' tunnels. 650 feet below ground at its deepest point, it was built to accommodate broad gauge and formed part of the 6¼-mile Gelli Tarw Junction-Merthyr extension, opening on 2nd November 1853. It regularly takes two names - Merthyr, which is to its east, and Abernant.