After the defeat of Xerxes at Salamis, the Athenian general Themistocles claimed that the Greek victory was the result of divine intervention since the gods and heroes “did not want to see a single man ruling both Asia and Europe”. The ancient sources are full of traditions of Greeks offering thanks to various gods for their assistance. Demeter, the provider of grain and founder of the Mysteries, was not a martial goddess, her contribution to Greek victory was nonetheless substantial and crucial. According to Herodotus, Demeter helped the Greeks in Plataea and Mycale, canonical Greek victories by land and sea. 

The most famous story, though, concerns a miraculous apparition on the eve of the battle of Salamis in 480 BCE. The Persian army was in the process of devastating the Thriasian Plain when Dikaios, an exiled Athenian in the service of Xerxes, noticed an enormous cloud of dust heading towards them from Eleusis as if raised by the march of thirty thousand men. Dikaios knew that the Athenians had abandoned Attica, so he wondered at the cause of this cloud. Suddenly he heard a voice that seemed to be the mystic “Iacchus”. Demaratus, an exiled Spartan also in the service of King Xerxes and unfamiliar with the rites of Eleusis, asked him what was making this cry, and Dikaios replied that it was inevitable that a great disaster threatened the Persian army. Since Attica was deserted, the utterance was divine and was coming from Eleusis to avenge the Athenians. When the cloud turned towards the fleet at Salamis, it became apparent to Dikaios that the royal armada would soon be lost.

The story of this apparition demonstrates the widespread belief that the sacred Mysteries of Demeter had to be celebrated at the appropriate time. Dikaios felt that the cloud rose from the feet of thirty thousand men, a number Herodotus uses from the whole population of Athens at the time of the Persian invasion. The battle of Salamis took place in late September, at the time when the Mysteries were celebrated. Since the Athenians could not participate, a divine host of spirits replaced the mystai and marched with the cry of “Iacchus” before joining the Greeks in Salamis to defeat the arrogant Persians.