Archimedes was a Greek mathematician, astronomer, philosopher, physicist and engineer. He was killed by a Roman soldier during the sack of the city, despite orders from the Roman general, Marcellus, that he was not to be harmed. (The Greeks said that he was killed while drawing an equation in the sand, and told this story to contrast their high-mindedness with Roman ham-handedness; however, it should be noted that Archimedes designed the siege engines that devastated a substantial Roman invasion force, so his death may have been out of retribution.) Some math historians consider Archimedes to be one of history's greatest mathematicians, along with possibly Newton, Gauss, and Euler. Archimedes was a famous mathematician whose theorems and philosophies became world known. He gained a reputation in his own time which few other mathematicians of this period achieved. He is considered by most historians of mathematics as one of the greatest mathematicians of all time. He discovered pi. He was best known for his discovery of the relation between the surface and volume of a sphere and its circumscribing cylinder, for his formulation of a hydrostatic principle Archimedes' principle and for inventing the Archimedes screw (a device for raising water). Archimedes Principal states: an object immersed in a fluid experiences a buoyant force that is equal in magnitude to the force of gravity on the displaced fluid. He also invented things such as the hydraulic screw - for raising water from a lower to a higher level, catapult, the lever, the compound pulley and the burning mirror. In mechanics Archimedes discovered fundamental theorems concerning the center of gravity of plane figures and solids.