Amsterdam had acquired city rights in 1300. From the beginning of the 16th century, it grew to be the largest city in the Netherlands. Occupied by Alba in 1567, it joined the anti- Spanish alliance in 1578. From then on, the city had constantly to expand. The city council and four burgomasters, as the authority which alone made the final decisions, faced the questions of how far they could extend their territory in order to keep pace with the pressures of an increasing population, and at what point costs would exceed income. Every expansion involved century was engaged in comprehensive works for new dams, moats, and canals. They were always carried out according to the same principle of fanning the Amstel out into a delta, the extremities of which formed the fortification moats.