The name Cardiff may be an Anglicisation of the Welsh name "Caerdydd". There is uncertainty concerning the origin of "Caerdydd"—"Caer" means "fort" or "castle," but although "Dydd" means "Day" in modern Welsh, it is unclear what was meant in this context. Some believe that "Dydd" or "Diff" was a corruption of "Taff", the river on which Cardiff castle stands, in which case "Cardiff" would mean "the fort on the river Taff" (in Welsh the T mutates to D).
Others favour a link with Aulus Didius Gallus, as it is known that the Romans established a fort in Cardiff when he was governor of the nearby province, in which case Cardiff might mean "the Fort of Didius". A Norman castle still exists, within the site of the earlier Roman fort, but was substantially altered and extended during the Victorian period by John Crichton-Stuart, 3rd Marquess of Bute, and the architect William Burges. Original Roman work can, however, still be distinguished in the wall facings.
There is a second castle north of the city, called Castell Coch (Welsh: "the Red Castle"). The current castle is an elaborately decorated Victorian folly designed by Burges for the Marquess and built in the 1870s. However, the Victorian castle stands on the footings of a much older medieval castle possibly built by Ifor Bach, a regional baron with links to Cardiff Castle also. The exterior has become a popular location for film and television productions.
Situated on the narrowest part of the south Wales coastal plain, Cardiff had a crucial strategic importance in the wars between the Normans (who had occupied lowland Wales) and the Welsh who maintained their hold on the Uplands. As a result Cardiff claims to have the largest concentration of castles of any city in the world. As well as Cardiff Castle and Castell Coch the remains of Castell Morgraig, Bishop's Castle, Y Twmpath, Ruperra Castle and Saint Fagans Castle are still in existence while Whitchurch Castle and King's Castle have disappeared under later developments.
Cardiff has a chequered linguistic history with Latin, English, Welsh, and Norse dominating at different times. Although it was the Romans who established the "castle on the Taff" it was the Vikings who first began developing the maritime trade from which the town (later to become a city) was to derive its prosperity. The Vikings - who controlled the Bristol Channel - used Cardiff as a raiding base, a port and a trading post. Many street-names in Cardiff are of Viking origin including Dumballs Road and the oldest street in the city, Womanby Street. Womanby Street is a corruption of the original Norse name Humandaby Street. Some believe that Welsh was the majority language from the thirteenth century until the city's explosive growth in Victorian times. As late as 1850 five of the twelve Anglican churches within the current city boundaries conducted their services exclusively in Welsh, while only two worshipped exclusively in English.