Much of the Amsterdam canal system is the successful outcome of city planning. In the early part of the 17th century, with immigration rising, a comprehensive plan was put together, calling for four main, concentric half-circles of canals with their ends resting on the IJ Bay. Known as the "grachtengordel",[5] three of the canals are mostly for residential development (Herengracht or ??Patricians' Canal??; Keizersgracht or ??Emperor's Canal??; and Prinsengracht or ??Prince's Canal??), and a fourth, outer canal, Singelgracht, for purposes of defense and water management. The plan also envisaged interconnecting canals along radii; a set of parallel canals in the Jordaan quarter (primarily for the transportation of goods, for example, beer); the conversion of an existing, inner perimeter canal (Singel) from a defensive purpose to residential and commercial development; and more than one hundred bridges. The defensive purpose of the Nassau/Stadhouderskade was served by moat and earthen dikes, with gates at transit points but otherwise no masonry superstructures.[6]
