The road between London and Holyhead, the packet port for Dublin on the island of Anglesey in north Wales, was improved on an heroic scale between 1815 and 1840, under the direction of a commission established by parliament with Sir Henry Parnell (1776-1842) as its chairman and Thomas Telford (1757-1834) as its engineer. The project arose from strategic needs, and from complaints about existing roads by Irish members of parliament who, after the Act of Union, attended parliament in London. For 240 km from London to Shrewsbury the commission worked with turnpike trusts to improve the route, but for the 170 km from Shrewsbury to Holyhead it took direct control of the road. In the late 1990s Cadw recognised the significance of the road and has taken steps to ensure the appropriate protection of features along the 133 km stretch from the English border at Chirk to Holyhead, as well as commissioning a report that has set new standards in the investigation of historic routeways in the United Kingdom, and commencing a programme of interpretation.
While many of Telford’s improvements can still be studied on the English section of the road that runs from London through St Albans, Dunstable, Stony Stratford, Daventry, Coventry, Birmingham, Wolverhampton, Shrewsbury and Oswestry, the most spectacular monuments are to be found in Wales. These include the Menai Suspension Bridge, a wholly new stretch of road across Anglesey of the early 1820s with a purpose-built coaching inn at Mona, the passes of Nant Ffrancon and Glyn Diffwys, the cast-iron Waterloo Bridge at Betws-y-Coed, and the Stanley Embankment at Holyhead. Through the mountains of North Wales long stretches of the road conform to a section drawing used by Telford in his autobiography, and are protected by retaining walls on the uphill side and by stone parapets on the downhill side. The road is still lined by tollhouses and mileposts of standard design, together with ‘depots’, the recesses used for the storage of road metals before the introduction of bonded surfaces.