The A5, the London-Holyhead trunk road, is a major road in England and Wales. It runs for about 243 miles (391 km) from London to the Irish Sea at the ferry port of Holyhead. In many parts the route follows that of the Roman Iter II route which later took the Anglo-Saxon name Watling Street.

Watling Street is a historic route in England that crosses the River Thames at London and which was used in Classical Antiquity, Late Antiquity, and throughout the Middle Ages. It was used by the ancient Britons and paved as one of the main Roman roads in Britannia. The route linked Dover and London in the southeast, and continued northwest via St Albans to Wroxeter. The line of the road was later the southwestern border of the Danelaw with Wessex and Mercia, and Watling Street was numbered as one of the major highways of medieval England.