The Romans built a fort at Cardiff in about 75 AD. The Normans later used the same site to build Cardiff Castle in the 12th century.
Until the building of the Glamorgan Canal in 1794, Cardiff was a relative small town. The canal linked the ironworks and coalmines of the Merthyr Tydfil district with Cardiff on the coast. By 1821 Cardiff had 3,579 inhabitants, which made it the 27th largest town in Wales.
The first dock was built in 1839 and this increased the amount of trade taking place in Cardiff. By this time Merthyr Tydfil was the largest iron producing area in the world. Two of the owners of these ironworks, Josiah Guest and Anthony Hill, joined forces to form the Taff Vale Railway Company. Isambard Brunel, a talented engineer from Bristol, was recruited to build the railway.
The Taff Vale Railway was completed in 1841. It was now possible to transport goods from Merthyr Tydfil to Cardiff in less than an hour. Later, branches were built to link the mining valleys with Welsh ports and England's fast growing industrial towns and cities. The railway network reduced transport costs so much that it was now profitable to export Welsh coal to countries as far away as Argentina and India.
The East Dock was opened in 1859, and by 1861 the population had reached 33,000, making Cardiff the most important town in Wales.
The 20th century saw the emergence of several new buildings including the City Hall (1906), the Law Courts (1906), the National Museum of Wales (1927) and the Welsh Office (1938).
Landaff and Cardiff stand almost together. Landaff is the seat of the episcopal see, and a city, but Cardiff which is lower on the river, is the port and town of trade; and has a very good harbour opening into the Severn Sea, about four miles below the town.