Watford Gap is a low-lying area between two hills, close to the village of Watford, Northamptonshire, England. Engineers from Roman times onwards have found it to be an ideal route for connecting the Midlands with South East England. The A5 road, the West Coast Main Line railway, the M1 motorway and a branch of the Grand Union Canal traverse in parallel a space about 400 metres (1,300 ft) wide. It has been written and spoken of as marking the divide between Northern England and Southern England.

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.