Despite the ongoing effort by both church and government to assimilate and convert the Ifugao, they have remained remarkably unchanged. The Ifugao, who number approximately 120,000, live in widely scattered groups over some 750 square miles of rugged, precipitous terrain where heavy rainstorms are frequently followed by slides, flash floods and washouts. They are an agrarian people deeply involved with the growing of rice, the ritual and magic which surrounds it, and in maintaining the ways of the revered ancestors. In farming their unstable and harsh country, the Ifugao have acquired a thorough familiarity with local drainage patterns. Their understanding of hydraulic technology, combined with excellent stonemasonry skills and the simplest of hand tools, have enabled them to create the world's most extraordinary system of rice terracing. Ifugao rice terraces are sturdy stone walls which can reach as high as 50 feet, and are constructed along the land's natural contours. When finished, the terraces are backfilled and another wall at a slightly higher elevation is constructed. By repeating this process from valley floor to mountain peak, the Ifugao are able to construct their rice fields on the steepest of slopes. But sites are selected carefully, because the terraces require an elevated water source to flood the fields during the growing season. An elevated water source is also of great assistance during initial construction. The dammed water can be released to assist in moving the many tons of boulders, stones and earth required in a new terrace. Irrigation water is frequently brought from great distances by ingenious stone-lined channels and hollow log or bamboo aquaducts that cross canyons and chasms and snake around the sides of mountains. Rice to the Ifugao is something more than basic sustenance. Over countless generations they have created a balanced, stable society based on rice as a medium of exchange, power and subsistance. Ifugao social status is inexorably linked to the amount of rice harvested, terraces built and all-round good management and business acumen. Although the mountains yield frugally at the cost of much labor, the production of rice and the building of thousands of miles of stone terracing and irrigation systems are regarded by the Ifugao as a physical manifestation of ritual energy and group cohesiveness. With the help of the ancestors and other spiritual beings (called up on a complex cycle of agricultural rituals and ceremonies), the Ifugao have transformed high mountains and deep ravines into vertical, verdant fields that have allowed them to prosper and remain independent of the vagaries of national politics. Bound strongly by family ties and the need to be near their fields, the Ifugao live in small, loosely confederated settlements of identical thatched roofed houses. Many years ago, fierce rivalry and constant inter-valley feuding caused villages to be bunched in relatively inaccessible but easily defended locations, but now in more tranquil times, villages are found perched on top of prominent peaks, carefully wedged into steep mountainsides or clustered in valleys. Small, but well constructed, Ifugao houses are appropriate for a people close to the land and to each other. Insofar that the greater part of Ifugao life takes place outdoors, little more is required than storage for a few possessions, a place to sleep, and a shelter in which to rest and cook during inclement weather. In housebuilding, as with most other aspects of traditional Ifugao life, form is dictated by custom and convention.