Wisdom from the Early Stoics, Zeno of Citium 3

He used then to discourse, pacing up and down in the painted colonnade, which is also called the colonnade or Portico of Pisianax, but which received its name from the painting of Polygnotus; his object being to keep the spot clear of a concourse of idlers. It was the spot where in the time of the Thirty 1400 Athenian citizens had been put to death. 

Hither, then, people came henceforth to hear Zeno, and this is why they were known as men of the Stoa, or Stoics; and the same name was given to his followers, who had formerly been known as Zenonians. So it is stated by Epicurus in his letters. According to Eratosthenes in his eighth book On the Old Comedy, the name of Stoic had formerly been applied to the poets who passed their time there, and they had made the name of Stoic still more famous. 

—Diogenes Laërtius, 7.5