In any history of the natural law the Stoics occupy an important place. There is general agreement that they were the first to systematize the concept, although not all would agree with the comment of Samuel Pufendorf (1632–1694), himself a key-figure in the modern shaping of the natural law, that the Stoic concept had been narrowed by the substitution of Aristotle's philosophy of law and politics for the Stoic ideas.¹ But which Stoics? And what was their conception of the natural law? These are questions not easily answered when one recalls that the school stretches over half a millenium and includes thinkers that differ even on matters one would have thought essential. Zeno of Citium (c. 336-264 b.c.) appeared at Athens, teaching at the painted porch (stoa poikile, whence the name" stoic") about the year 300 b.c. He and his first successors, Cleanthes (c. 331-233 b.c.) and Chrysippus (281-208 b.c.) constitute the Early Stoa. The Middle Stoa is represented mainly by Panaetius of Rhodes (c. 185-110 b.c.) and Poseidonius of Apamea (135-51 b.c.); and the Late or New Stoa covers the first to the third centuries a.d., the age of Seneca (3-65 a.d.), the former slave Epictetus (c. 60-100 a.d.) and the Emperor Marcus Aurelius Antoninus who reigned from 161 to 180 a.d.