Nisi Chrysippus fuisset, Porticus non esset. Chrysippus of Soli was a disciple of Zeno the Stoic, and Cleanthes his successor. He did for the Stoics what St. Paul did for Christianity- that is, he explained the system, showed by plausible reasoning its truth, and how it was based on a solid foundation. Stoicism was founded by Zeno, it is true; but if Chrysippus had not advocated it, the system would never have taken root.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894