He aided in the defense of his native city against the Romans in 212 B.C., and devised war-engines with which to repel the besiegers. After the enemy had entered the city, says tradition, he stood absorbed in a mathematical problem which he had diagrammed on the sand. As a rude Roman soldier approached, Archimedes cried, "Don't spoil my circles," and was instantly killed. The victorious general, however, buried him with honor, and on the tomb of the mathematician caused to be inscribed the sphere with its enclosing cylinder. The triumphs of Greek abstract thought teach the lesson that practical men should pay homage to speculation even when they fail to comprehend a fraction of it. REFERENCES Aristotle, _Historia Animalium_; translated by D'A. W. Thompson. (Vol. IV of the _Works of Aristotle Translated into English_. Oxford: Clarendon Press.) A. B. Buckley (Mrs. Buckley Fisher), _A Short History of Natural Science_. G. H. Lewes, _Aristotle; A Chapter in the History of Science_. T. E. Lones, _Aristotle's Researches in Natural Science_. D'A. W. Thompson, _On Aristotle as a Biologist_. William Whewell, _History of the Inductive Sciences_. Alfred Weber, _History of Philosophy_. CHAPTER III SCIENTIFIC THEORY SUBORDINATED TO APPLICATION--ROME: VITRUVIUS Vitruvius was a cultured engineer and architect. He was employed in the service of the Roman State at the time of Augustus, shortly before the beginning of the Christian era. He planned basilicas and aqueducts, and designed powerful war-engines capable of hurling rocks weighing three or four hundred pounds. He knew the arts and the sciences, held lofty ideals of professional conduct and dignity, and was a diligent student of Greek philosophy.