Cardiff in making iron and later steel, brought to the sea by packhorse from Merthyr Tydfil. This was first achieved by the construction of a long canal from Merthyr (510 feet above sea-level) to the Taff Estuary at Cardiff. Eventually the Taff Vale Railway replaced the canal barges and massive marshalling yards sprang up as new docks were developed in Cardiff – all prompted by the soaring worldwide demand for coal from the South Wales valleys. At its peak, Cardiff's port area, known as Tiger Bay, became the busiest port in the world and – for some time – the world's
Cardiff at the eastern end of the city centre, and also provides services to Cardiff Bay. Cardiff has a suburban rail system known as the Valleys & Cardiff Local Routes, which is operated by Transport for Wales. There are eight lines which serve 20 stations in the city, 26 in the wider urban area (including Taffs Well, Penarth and Dinas Powys) and more than 60 in the South Wales valleys and the Vale of Glamorgan. Domestic and international air links to Cardiff and South & West Wales are provided from Cardiff Airport (CWL), the only international airport in Wales. The airport