In precontact times the majority of the Emberá population lived in dispersed settlements along the rivers. There was a difference between the Emberá of the alluvial plains, who settled on high terraces of the river banks, and the Emberá of the slopes, who, because of the uneven nature of the terrain, settled on the median and high parts of the hillsides, as well as on the scarce fertile flood plains of some rivers. Spanish chroniclers also recorded a number of nucleated villages on the Río Atrato. The necessity of letting fields lie fallow after cultivation is the basic condition of Emberá shifting cultivation, imposing a pattern of accentuated mobility over large tracts of land. In some peripheral areas the Indians have experienced a scarcity of land and traditional horticulture has deteriorated. Efforts by missionaries and the Organización Regional Emberá y Waunana (Regional Organization of Emberá and Waunana) have resulted in the construction of villages of between ten and fifty houses. There are schools, shops, health clinics, and, sometimes, a church and electricity. Occupation is not on a permanent basis; each family lives in the village for only a portion of the year. Most of their time is spent on their remote upriver plots, several hours away by canoe. The tambo , their traditional house form, is a large pile dwelling several meters above ground, with a rectangular floor of palm stems or bamboo and a conical roof of palm thatch that reaches down between 0.5 and 1 meter above the platform, obviating the need for walls. On the floor there are one or several hearths of clay. The Indians are slowly adopting rustic houses made of boards, with zinc, bamboo, or asbestos-cement roofs and earthen floors; there are walls and windows and several interior rooms separated by wooden dividers.