Holy Island (in Welsh, Ynys Cybi, "the island of St. Cybi") is a small island (approx. 8x4 miles) on the western side of Anglesey, Wales, to which it is connected by causeways carrying the A5/A55 road and the main railway line to Chester and London, and the original bridge of the A5 post road. It is so called because of the high concentration of standing stones, burial chambers and other religious sites. The main settlement is the port of Holyhead, from which passenger ferries travel to Dun Laoghaire and Dublin, Ireland, and freight ferries also travel to Dublin. Peripheral islands and stacks include South Stack, with its famous lighthouse. Before, and even after the construction of lighthouses, the cliffs and jagged rocks of the island were a great danger to seamen.