The plow—or plough—one of the oldest types of agricultural implements, is used to break up soil in preparation for planting. Modern plows are also used to bury, or plow under, crop remains at the end of the growing season.

The earliest plow was the swing plow (a plow without wheels) used in Egypt and Mesopotamia by about 4000 b.c. Civilizations that did not have the plow had to do their planting either by broadcasting the seed onto soil without burying it--which wastes a great deal of seed--or by planting seeds one at a time with a stick or sharp piece of antler. The first wheeled plow was developed in what is now Switzerland during the first century b.c. The wheels gave the plow weight and stability and also gave the furrow a more even depth.

The first iron plowshare—the share is...