A tool designed to be drawn through the ground to break it up for cultivation, often powered by a yoke (or more) of oxen, other animals, or men. The earliest type of plow, developed from the hoe and digging stick, is the ard or scratch plow, which stirs the soil without turning it. Cross-plowing, the result of a second plowing at right angles to the first, is usually necessary. This type was of Near Eastern origin c 4th millennium BC. The later plow, heavier and wheeled, did not appear until the early centuries AD. It is more suited to the heavier soils of Europe. Prehistoric America, lacking suitable draft animals, did not have a plow. The 18th-century addition of the moldboard, which turned the furrow slice cut by the plowshare, was an important advance. The plow is considered the most important agricultural implement of history, used to turn and break up soil, to bury crop residues, and to help control weeds.