The A2 is a major road in south-east England, connecting London with the English Channel port of Dover in Kent. This route has always been of importance as a connection between London and sea trade routes to Continental Europe. It was originally known as the Dover Road. The M2 motorway has replaced part of the A2 as the strategic route. Unlike the other single digit A-roads in Great Britain, the A2 does not form a zone boundary. The boundary between Zones 1 and 2 is the River Thames. History of the route The route of the current A2 follows a similar route to that of a Celtic ancient trackway. It was an important route for the Romans linking London with Canterbury and the three Channel ports of Rutupiae (now Richborough), Dubris (now Dover) and Portus Lemanis (in modern Lympne). It had river crossings at Rochester over the River Medway; Dartford (River Darent) and Crayford (River Cray). The Romans paved the road and constructed the first Rochester Bridge across the Medway. Access to London was via London Bridge which was first constructed by the Romans in AD 50. The road appeared in the Antonine Itinerary, a contemporary map of Roman roads in Britain, as 'Item a Londinio ad portum Dubris'. In Anglo-Saxon times it became part of a longer road known as Wæcelinga Stræt ('Watling Street' in modern English). Rochester Bridge was rebuilt in stone in 1391 and the 'Wardens and Commonalty of Rochester Bridge' were created to maintain the bridge, the modern equivalent of which, the Rochester Bridge Trust, still manages the current crossing. By the 17th century, the road had fallen into disrepair and sections were converted into turnpike roads by various Turnpike Acts passed by Parliament. The section between Gravesend and Rochester was turnpiked in 1712 and that from Chatham to Canterbury in 1730; the section from there to Dover was only turnpiked in the 19th century by which time it was known as the Great Dover Road. Rochester Bridge was rebuilt in cast iron in 1856 (and rebuilt again in 1914 with a second bridge in 1970). The London, Chatham and Dover Railway completed a railway route from London to Dover in the 1860s. Access to London from the A2 across the River Thames was improved with the completion of Tower Bridge (1894), Blackwall Tunnel (1897) and the Rotherhithe Tunnel (1908). The road was given the reference