Merthyr Tydfil, at the northern end of the Taff valley, became Wales's largest town thanks to its growing ironworks at Dowlais and Cyfarthfa. The neighbouring Taff Bargoed Valley to the east became the centre of serious industrial and political strife during the 1930s, especially in and around the villages of Trelewis and Bedlinog, which served the local collieries of Deep Navigation and Taff Merthyr. The South Wales coalfield attracted huge numbers of people from rural areas to the valleys; and many rows of terraced housing were built along the valley sides to accommodate the influx. The coal mined in the valleys was transported south along railways and canals to Cardiff, Newport and Swansea. Cardiff was soon among the most important coal ports in the world, and Swansea among the most important steel ports.