Plutarch, Parallela minora
Frank Cole Babbitt, Ed.

The People of Sardis, when they were engaged in war against the people of Smyrna, encamped round about the walls, and sent word through ambassadors that they would never retire unless the people of Smyrna would agree to let their wives consort with them. The Smyrnaeans, because of the compelling necessity, were in a fair way to suffer grievously ; but there was a certain maid-servant to one of the better class who ran up to her master Philarchus and said, ‘You must dress up the maid-servants and send them in place of free-born women.’ And this, in fact, they did. The men of Sardis were quite exhausted by the serving-maids, and so were taken captive ; whence even now the people of Smyrna have a festival called Eleutheria in which the maid-servants wear the adornments of free women. So Dositheiis in the third book of his Lydian History. [p. 301]

When Atepomarus, king of the Gauls, was at war with the Romans, he said he would never retire unless the Romans should surrender their wives for intercourse. But the Romans, on the advice of their maid-servants, sent slave-women; and the barbarians, exhausted by unremitting intercourse, fell asleep. But Rhetana (for she had been the author of this advice), by taking hold of a wild fig-tree, climbed upon the wall and informed the consuls ; and the Romans attacked and conquered. From this the Servants' Festival takes its name.¹ So Aristeides the Milesian in the first book of his Italian History.