How much of the complete system known in later times under this name was due to Zeno himself, we do not know; for nothing but a few fragments of his and of his immediate successors’ writings is left. The idea of combining Antisthenes with Heracleitus, and both with Socrates, probably belongs to the founder of the school. His successor, Cleanthes, a man of character rather than of intellect, was content to hand on what the master had taught. Then came another Cypriote, Chrysippus, of whom we are told that without him the Stoa would not have existed;[16] so thoroughly did he work out the system in all its details, and so strongly did he fortify its positions against hostile criticism by a framework of elaborate dialectic. ‘Give me the propositions, and I will find the proofs!’ he used to say to Cleanthes.[17] After him, nothing of importance was added to the doctrines of the school; although the spirit by which they were animated seems to have undergone profound modifications in the lapse of ages. In reality, Stoicism was not, like the older Greek philosophies, a creation of individual genius. It bears the character of a compilation both on its first exposition and on its final completion. Polemo, who had been a fine gentleman before he became a philosopher, taunted Zeno with filching his opinions from every quarter, like the cunning little Phoenician trader that he was.[18] And it was said that the seven hundred treatises of Chrysippus would be reduced to a blank if everything that he had borrowed from others were to be erased. He seems, indeed, to have been the father of review-writers, and to have used the reviewer’s right of transcription with more than modern license. Nearly a whole tragedy of Euripides reappeared in one of his ‘articles,’ and a wit on being asked what he was reading, replied, ‘the _Medea_ of Chrysippus.’[19]