The Thai have always been an agricultural people of the lowland valleys and intermontane basins, where they cultivated wet rice with the use of water buffalo and harvested a wide range of fish and shellfish from the rivers and the sea. These occupations were often supplemented, especially in the north and northeast, by the collection of forest products, ranging from timber, such as teak and bamboo, to foods stored for consumption during the dry season. In the northern mountain valleys, Tai-speaking peoples developed an intricate system of small-scale irrigation, called muang fai. The eventual move to the great central plain necessitated the development of canals for transportation and, from the late-19th century onwards, of much larger irrigation and flood-control systems. Small nuclear families occupied villages, comprising a wat and wooden houses on stilts. The pattern of life was governed above all by the seasonal rhythm of the monsoons and by a series of important religious festivals. Many of these festivals were closely associated with fertility and the arrival and ending of the rains.