Primitive peoples raised crops on a cultivated plot until the land lost its fertility; then they moved to a virgin piece of ground where they cut down (“slash”) natural vegetation and burned off the stubble to clear the land. In many cases, the slash-burn-cultivate cycle was no more than a year in length, and few found a piece of ground anywhere that could support successful cropping for more than five years without fertilization. In farming villages, developed in ancient times and prevalent throughout the Middle Ages, innovation in fertilization was demanded, because the same land had to be used for many years. With the use of legumes in crop rotations, manures, dead fish, or almost any organic matter available, the land was kept in production.