_Zeno_ was born at Citium, a city of Cyprus; but having been shipwrecked near Cyprus, he settled in that city, where he devoted himself to severe study for a great length of time, cultivating, it is said, the acquaintance of the philosophers of the Megaric school, Diodorus and Philo, and of the Academics, Xenocrates and Polemo. After he had completed his studies, he opened a school himself in the porch, adorned with the paintings of Polygnotus (Στοὰ ποικίλη), from which his followers were called Stoics. The times of his birth and of his death are not known with any exactness; but he is said to have reached a great age. In speaking of the Stoic doctrines, it is not very clear how much of them proceeded from Zeno himself, and how much from Chrysippus and other eminent men of the school in subsequent years. In natural philosophy he considered that there was a primary matter which was never increased or diminished, and which was the foundation of everything which existed: and which was brought into existence by the operative power,—that is, by the Deity. He saw this operative power in fire and in æther as the basis of all vital activity, (see Cic. Acad. i. 11, ii. 41; de Nat. Deor. ii. 9, iii. 14,) and he taught that the universe comes into being when the primary substance passing from fire through the intermediate stage of air becomes liquefied, and then the thick portion becomes earth, the thinner portion air, which is again rarefied till it becomes fire. This fire he conceived to be identical with the Deity, (Cic. de Nat. Deor. ii. 22,) and to be endowed with consciousness and foresight. At other times he defined the Deity as that law of nature which ever accomplishes what is right, and prevents the opposite, and identified it with unconditional necessity. The soul of man he considered as being of the nature of fire, or of a warm breath, (Cic. Tusc. Quæst. i. 9; de Nat. Deor. iii. 4,) and therefore as mortal. In ethics he agreed with the Cynics in recognising the constitutional nature of moral obligations, though he differed from them with respect to things indifferent, and opposed their morose contempt for custom, though he did not allow that the gratification of mere external wants, or that external good fortune, had any intrinsic value. He comprised everything which could make life happy in virtue alone (Cic. Acad. i. 10), and called it the only good which deserved to be striven after and praised for its own sake (Cic. de Fin. iii. 6, 8), and taught that the attainment of it must inevitably produce happiness. But as virtue could, according to his system, only subsist in conjunction with the perfect dominion of reason, and vice only in the renunciation of the authority of reason, he inferred that one good action could not be more virtuous than another, and that a person who had one virtue had all, and that he who was destitute of one was destitute of all.