1. Erechtheus was a semi-divine legendary king of Athens who, inter alia, instituted the worship of Athena and Poseidon at Athens. lacchus was a deity associated with the mystery cult of Demeter at Eleusis. Just before the crucial battle of Salamis (480) against the Persians, the shout of ‘lacchus’ swept in the form of a cloud from Eleusis over the Persian fleet, signalling its impending defeat (Herodotus, 8.65). Athena and Poseidon could be said to be present, because Athena was guardian of the city, and Poseidon’s domain was the sea (Salamis being a sea-battle).
2. The festival referred to must be the Panathenaea, the occasion of this dinnerparty (p. 227). Callias was also a hereditary torch-bearer at the Eleusinian festival.