Anglesey. Island county of north-west Wales, separated from the mainland by the Menai Straits. In 1974 it became the district of Ynys Môn in the county of Gwynedd, but was reconstituted as a county in 1996. Its location, together with the protective barrier of the Snowdonian mountains, made it a traditional centre of resistance to invaders, Roman and Norman. But after conquest by Edward I it was created a county of the principality of Wales in 1284, a status confirmed at the Act of Union of 1536.

Anglesey is a low plateau with hills rising no more than 500 feet. It was known as ‘Môn mam Cymru’ (Môn, mother of Wales) because of its productive cereal-growing, but present farming is primarily dairy. Economic development is also related to the major road/rail crossings of the island to the port of Holyhead, the major British link to Ireland. Two bridges cross the Menai Straits; Telford's Menai suspension bridge (1819–20) and Stephenson's Britannia tubular bridge (1846–50), originally rail but now both rail and road. Copper was mined on Anglesey but recent economic activity is related to a nuclear power station at Wylfa Head and an aluminium smelter. Tourism is also a significant employer, mainly along the coastline.

The population of the county was 69,149 in 1991. The island has been one of the cores of Welsh speech: 91.7 per cent spoke Welsh in 1901, a figure fallen to 62.0 per cent in 1991.

Harold Carter

Anglesey (Ynys Môn) Island off the nw coast of Wales, separated from the mainland by the narrow Menai Strait. Formerly a Welsh county, it became part of Gwynedd in 1974. The chief town is Beaumaris, famous for a moated castle built by Edward I (1295). Holyhead is a major ferry terminus for Ireland. Area: 718sq km (276sq mi). Pop. (2001) 66,829.

Anglesey an island of North Wales, which in the 1st century ad was a centre of Druid power and resistance to Roman invasion; in ad 61 it was attacked by Suetonius Paulinus, who killed Druid priests and cut down sacred groves.