The center of gravity of a body or system of bodies is the point of application of the resultant of the weight-forces of the different components of the body or system. Archimedes (287-212 B.C.E.) wrote the first treatise on centers of gravity. His researches were revived and expanded in the sixteenth century by many mathematicians including Galileo (1564-1642), who took the Archimedean investigations into the centers of gravity of plane figures and extended them to solids.