That a monument of this kind could be transformed into an Olympian god is astounding

- Walter Burkert


Read the article from Wikipedia on Hermai. 

Or check out this info from the ancients:

Herodotus, Histories 2.51:

"The ithyphallic images of Hermes [the Hermai]; the production of these came from the Pelasgians, from whom the Athenians were the first Greeks to take it, and then handed it on to others. For the Athenians were then already counted as Greeks when the Pelasgians came to live in the land with them and thereby began to be considered as Greeks. Whoever has been initiated into the rites of the Kabeiroi, which the Samothrakians learned from the Pelasgians and now practice, understands what my meaning is [the Kabeiroi gods were the keepers of a sacred phallus]. Samothrake was formerly inhabited by those Pelasgians who came to live among the Athenians, and it is from them that the Samothrakians take their rites. The Athenians, then, were the first Greeks to make ithyphallic images of Hermes, and they did this because the Pelasgians taught them. The Pelasgians told a certain sacred tale about this, which is set forth in the Samothrakian mysteries."

Aesop, Fables 564 (from Babrius 48):

"There was a four-cornered statue of Hermes by the side of the road, with a heap of stones piled at its base." 




Pausanias, Guide to Greece 1.17.2:

"In the gymnasium not far from the market-place, called Ptolemy's from the founder, are stone Hermai well worth seeing." 

Pausanias, Guide to Greece 1.24.3:

"The Athenians are far more devoted to religion than other men ... they were the first to set up limbless Hermai." 

Pausanias, Guide to Greece 2.38.7:

"At the Arkadian gate [of Ithome, Messenia] leading to Megalopolis is a Herma of Attic style; for the square form of Herma is Athenian, and the rest adopted it thence."

Pausanias, Guide to Greece 4.33.3:

"Mount Parnon, on which the Lakedaemonian border meets the borders of the Argives and Tegeatai [of Arkadia]. On the borders stand stone figures of Hermes, from which the name of the place is derived."