From Project Athinai
The Stoa Poikile (Painted Portico) was built, by Peisianax, around 465 BC at the north extremity of the Agora, facing south. It was made mostly of various types of limestone. Its outer columns were of the Doric order and its inner ones of the Ionic order. The capitals of the Ionic columns were made of marble.
Soon after its construction, the stoa served as a gallery to expose famous paintings on wooden panel. Among them, the painting of the Battle of Marathon by Mikon and Panainos dating from around 460 BC, was described by Pausanias as follows:
The last part of the painting consists of those who fought at Marathon. The Boeotians of Plataia and the Attic contingent are coming to grips with the barbarians; at this point the action is evenly balanced between both sides. In the inner part of the fight the barbarians are fleeing and pushing one another into the marsh; at the extreme end of the painting are the Phoenician ships and the Greeks killing the barbarians who are tumbling into them. In this picture are also shown Marathon, the hero after whom the plain is named, Theseus, represented as coming up from the earth, Athena and Herakles -- the Marathonians, according to their own account, were the first to recognize Herakles as a god. Of the combatants, the most conspicuous in the picture is Kallimachos, who was chosen by the Athenians to be polemarch, and of the generals, Miltiades.
There were also paintings, dating of the same years, of Theseus against the Amazons by Mikon, of the sack of Troy by Polygnotos of Thasos and another about the victory of Oenoe over the Spartans and Argives.
Shields captured from the Spartans at Sphacteria in 425 BC were also exposed inside the stoa. These shields carried the following punched inscription: "The Athenians from the Lakedaimonians at Pylos".
The stoa had no specific administrative function, it served as a meeting place for the population. The presence of crowds in this area attracted philosopers, sword-swallowers, jugglers, beggars, parasites and fishmongers. The stoa might have been used as court once in a while and, once a year, it was used to summon the participants to the Eleusinian mysteries.
About 300 BC, the philosopher Zeno of Cyprus often used this stoa as his classroom. Consequently, his followers became known as Stoics.
American School of Classical Studies at Athens; The Athenian Agora: A Guide to the Excavation and Museum, 1990
Camp, John M.; The Archaeology of Athens, Yale University Press, 2001, pp. 68-69
Connolly, Peter and Hazel Dodge; The Ancient City - Life in Classical Athens & Rome, Oxford: Oxford University Press, 1998
Davis, W. S.; A Day in Old Athens, 1910
Hurwit, Jeffrey M.; The Acropolis in the Age of Pericles, Cambridge: Cambridge University Press, 2004
Tarbell, F. B.; A History of (Ancient) Greek Art, Chicago, 1905