In lowlands where irrigated rice was the basis of subsistence, settlements were distributed along waterways before the introduction of highways and railroads during the Spanish period. As this network of roads and railroads expanded, housing was extended along them even in upland areas where houses were usually dispersed in clusters oriented to landholdings and water supply. In both areas larger settlements served as markets and religious centers. Coastal settlements were clusters near sources of fresh water. Nonunilineal kinship ties were, and still are, foci for neighborhood and community. With the introduction of Roman Catholicism under the Spanish, the settlements became centralized around a church, chapel, or shrine (possibly continuing pre-Spanish patterns). By the beginning of the nineteenth century the larger settlements had complex central plazas with concentrations of population. Manila and several of the provincial capitals developed into urban centers. The houses have been of two major types: movable and nonmovable. Movable houses were built on stilts of bamboo and wood with thatch or metal roofs. Until recently, masonry houses were built mostly in the towns and cities. Manila and the other urban centers of the Tagalog area are rapidly becoming truly metropolitan districts. Manila, though an integral part of Tagalog society, is also a nexus for integration of almost all segments of the nation.