The institution of the Great Panathenaea was one of the central events in the religious life of Athens in the 6th с. ВС. However, the cult myth, the aition of this principal polis festival is only vaguely outlined in the figure of Erichthonius, the mythical founder of the Panathenaea. This figure was an innovation of the Attic mythology. The earliest layer of mythology is reticent about Erichthonius, knowing only Erechtheus, king and forefather of the Athenians (II. 2, 546553; Od. 7, 80-81). Erechtheus' mythology was rooted in the real Athenian cult practice. That of Erichthonius is also connected with the Athenian cult realities (Athena's serpent abiding on the Acropolis and the sacred olive growing there - a reflex of the 'world tree' mythology with the obligatory serpent living in its roots). Athena's sacred olive grew on the sacred plot of Pandrosos, ancient Attic goddess of fertility, and the temple of her sister Aglauros stood on the slope of the Acropolis. For this reason in the myth the Cecropidae sisters turn to be nurses of the serpent-shaped child, and Athena nurses him in her temple as a kourotrophos as well. This element («a miraculous child nursed by goddesses») was initial in the myth of Erichthonius, from the moment when he ceased to be just a serpent and acquired a minimum of narrative characteristics. Another innovation of the myth is the episode of the suicide of Cecropidae, modelled after the pattern of «sacrifice of the king's daughters», reflected in the rite of Arrhephoria and incorporated into the initial myth of Erichthonius' birth. Why was it then necessary to construct the mythology of Erichthonius on the basis of Athens' sacred topography and fragments of other myths? In the author's opinion, the answer lies in the main mythical «act» of Erichthonius, i.e. the institution of the Panathenaea. Their real institution in 566/565 ВС is connected with the name of Peisistratos. The essence of his reforms of the Panathenaea consisted in transferring the ideological centre of the festival to its polis aspect, and the old agricultural and cosmogonic roots of the rite are still to be seen. Thus, it is Erechtheus' priest who holds the peplos offered to Athena on the frieze of the Parthenon. In the new «civilized» version of the ritual (as well as in the myth) the serpent living in the roots of the world tree is none other than Erichthonius, the founder of the Panathenaea and the inventor of the chariot (horse race was another important element of the festival). The Panathenaea were to compete with the Olympic Games, so Erichthonius became the founder of the chariot race to spite Pelops and Oenomaus with their chariot races, which made the cult myth of the Olympic Games. But according to the older Athenian mythology, the Panathenaea were founded by Theseus (Plut. Thes. 24). However, in Theseus' mythology the institution of the Panathenaea was just one of his acts, and not the most important one, while for Erichthonius the founding of the Panathenaea with chariot races became his only act apart from his birth and death, i.e. Erichthonius was modelled as the founder of the games par excellence. Obviously, the development of the myth of Erichthonius, an 'autochthon' and Athena's favorite, the inventor of the chartiot and founder of the Panathenaea, was directly connected with Peisistratos' wish to legitimate his power. In the 6th century ВС such legitimization was only possible in the form of a myth.