Holyhead (Welsh: Caergybi, "the fort of St. Cybi) is the largest town in the county of Ynys Môn (Anglesey) in the northwest of Wales, United Kingdom. Although it is the largest town in the county, it is not actually on the island of Anglesey but is instead located on Holy Island which is connected to Anglesey by Four Mile Bridge, so called because it is four miles from Holyhead on the old post road from London, and a causeway build by local philanthropist Lord Stanley in the nineteenth century, which now carries the A5/A55 road and the railway line to Chester, Crewe and London.
The town's centre is built around St. Cybi's church, which is built inside one of Europe's only three-walled Roman forts (the forth wall being the sea, which used to come up to the fort). The Romans also built a lighthouse on the top of Holyhead Mountain inside Mynydd y Twr, a prehistoric fortress. Settlements in the area date from prehistoric times, with circular huts, burial chambers and standing stones featuring in the highest concentration in Britain.
Holyhead is perhaps best known for its busy ferry port and freight harbour. Ferries sail to Dublin and Dún Laoghaire in Ireland and this forms the principal link for surface transport from central and northern England to Ireland. The post road built by Thomas Telford from London established Holyhead's port, from where the royal mail was dispatched to and from Dublin.
Holyhead's maritime importance was at its paramount in the nineteenth century when the two and a half-mile breakwater, widely acknowledged to be one of Britain's finest, was built, creating a safe harbour for vessels caught in stromy waters on their way to Liverpool and the industrial ports of Lancashire.
Today, Holyhead's main industry in aluminium-based, with Rio Tinto's Anglesey Aluminium subsidiary operating a massive aluminium smelter on the outskirts of the town. There is also a plant that refines bauxite near the site. A large jetty in the harbour receives ships from Jamaica and Australia, and their cargo of bauxite and aluminium ores are transported on a conveyor belt than runs underneath the town to the plants.