a port in Kent, south-east England, and the nearest English town to France. The part of the Channel between Dover and Calais (called the Strait of Dover) is 21 miles/34 kilometres wide and is one of the busiest sea routes in the world. The high white cliffs of Dover, which can be seen from a distance, have a special meaning to British people returning home by this route. Dover has a long history. It was a town in Roman times, and its castle, which was the administrative centre of the Cinque Ports, was an important part of the country's defences.