Giovanni Antonio Canaletto, The Thames and Westminster Bridge from the north, pen and ink with wash over black chalk

This splendid drawing is a reminder that the grandest approach to Westminster was by river - whether following tradition in a richly decorated shallop or passenger barge or taking advantage of the most striking addition to mid-eighteenth century London by crossing the new bridge. It was this elegant marvel of engineering that would have impressed the contemporary viewer. The palaces of Lambeth and Westminster, centres of ecclesiastical and political power, dominate the skyline, but their medieval architecture was of only antiquarian interest. The new Westminster Bridge not only opened up the western part of town, but also stood as a symbol for the shift of the capital away from the commercially focused City (with its ancient crowded bridge inhabited by shopkeepers) to a new identity as the home of political power on a global scale.Close examination reveals something of Canaletto's technique. The architecture is carefully constructed with ruled black chalk lines, and pinpricks indicate that the arches of the bridge have been measured with dividers. These guides are overlaid with lively detail freely drawn in pen and brown ink, and varied tones of grey wash create an illusion of three-dimensionality. The wooded hills on either side are compositional inventions.