The city initially consisted of a few precarious villages on a series of islands, physically separated from each other, yet forming a concentration of settlements along this vast archipelago. The city was not alone: many monasteries and other minor settlements were built in the lagoon area (some of which still remain, such as Torcello and Burano; others having disappeared, such as Costanziaca and Ammiana). Like Venice, all were located at points where the main rivers/canals met between the mainland and the sea.