Holyhead (nprn 32990) developed into a large town following the building of new roads and the Menai Bridge (by Thomas Telford in c.1801) to improve communications and travel from London to Dublin. In 1810 an Act of Parliament was passed which provided for necessary improvements to the harbour at Holyhead which had by then had become established as the principal port for communication with Ireland, and in particular was the station for the Post Office steam packets. This work involved the construction, under the supervision of John Rennie, of the Admiralty Pier and lighthouse and the Harbour-Master's Offices and Customs House, with the later addition of the George IV Arch. The works were completed in 1821.
By the 1840s the amount of coastal shipping using Holyhead had significantly increased and the harbour was deemed inadequate for the demands upon it. In the mid-1840s plans were mooted for a major 'new' harbour which would cover an area of 316 acres and be capable of accommodating up to 1,000 vessels. An important factor in this development was the Chester and Holyhead Railway which had been incorporated in 1844 and would bring much additional traffic - especially passengers and mail - to Holyhead.
In 1847/48 the 'Great Breakwater' began construction at Holyhead to provide one of the main protections for the new harbour. The Great Breakwater was to be 5,360 feet in length, while the secondary breakwater was to be 2,000 feet long. The supply of stone for the construction was found at Holyhead Mountain, at the north-west end of Holy Island. Work was completed in 1854, and the refuge it protected became formally known as the New Harbour. The earlier harbour became known as the Old Harbour. By 1857, due to increased demand on the facilities, the Great Breakwater was extended to a total length of 7,860 feet.
Following the creation of the Irish Free State in 1922, the town began to decline with the subsequent cessation of mail boats to Dublin. The port continued to operate, however, evolving to the ferry port it is today.
RCAHMW, 15 September 2011.