HOLYHEAD (Welsh, Caer Gybi, i. e., fort of Gybi), a parliamentary borough, seaport, and market-town of North Wales, on an island at the western extremity of the county of Anglesea. It is connected with the main part of the county by a vast embankment, three-quarters of a mile in length, and of an average height of 16 feet, with a bridge near the centre through which the tide rushes with amazing velocity and force. The town, formerly a small fishing village, has acquired importance in consequence of its being the nearest and most convenient place of embarkation for Ireland. It is the point of termination of the great parliamentary roads from London and Chester, and of the Chester and Holyhead railway, in connection with which steam-packets leave the harbour several times a-day for Kingston near Dublin. The vast amount of labour and money expended on public works connected with the harbour has materially contributed to attract and support an active and thriving population. Holyhead has been selected by government for a harbour of refuge. The works when completed will enclose an area of about 316 acres, with a depth of at least 6½ fathoms water. The church, occupying the elevated site of an ancient monastery, is dedicated to St Gybi; and in the south porch is a rude figure of the patron saint, under a canopy. The churchyard is partly surrounded by a very curious and interesting Roman wall. The pier extends nearly 1000 feet, and upon it is an arch of Mona marble commemorative of the visit of George IV. in 1821. At the extremity of the pier is a lighthouse, exhibiting a white light 50 feet above sea-level. On South Stack (Stack), an isolated rock 3 miles W., is another lighthouse connected with the harbour, and of essential service in facilitating the access. The light, which is 212 feet above high-water mark, is produced by 21 lamps with powerful reflectors. The inhabitants are chiefly engaged in the coasting trade and in shipbuilding. The coast is extremely wild and rugged, presenting numerous wave-worn caverns, which form the haunt of innumerable sea-birds. From the summit of Pen-Caer-Gybi, or the Mountain of Holyhead, 700 feet in height, a good view is obtained of the town and harbour. On the sides of the mountain are traces of extensive British fortifications, and at the top are remains of a circular building 10 feet in diameter, which was probably a Roman watch-tower. Market-day, Saturday. The borough is contributory to Beaumaris in returning a member to parliament. Pop. (1851) 5622.