Chiomara was a chieftain's wife from Galatia (Asiatic Gaul or the Gaul of the East) whom Polybius, Livy, and Plutarch describe. During the Galatian War of 189 B.C., she was captured by the Romans and fell into the hands of a greedy centurion. Like the pirates who captured Julius Caesar, her violator should have known there would be repercussions. Like the pirates, her violator paid with his life, but while the pirates were crucified [see Plutarch on Caesar and the Pirates], the decidedly monogamous Chiomara decapitated her rapist.

Here is the passage from Polybius, in English translation:

"38 Chiomara, the wife of Ortiagon, was captured with the other women when the Asiatic Gauls were defeated by the Romans under Manlius [Gnaeus Manlius Vulso]. 2 The centurion into whose hands she fell took advantage of his capture with a soldier's brutality and did violence to her. 3 The man was indeed an ill-bred lout, the slave both of gain and of lust, but his love of gain prevailed; and as a considerable sum had been promised him for the woman's ransom, he brought her to a certain place to deliver her up, a river running between him and the messengers. 4 When the Gauls crossed and after handing him the money were taking possession of Chiomara, she signed to one of them to strike the man as he was taking an affectionate leave of her. 5 The man obeyed and cut off his head, which she took up and wrapped in the folds of her dress, and then drove off. 6 When she came into the presence of her husband and threw the head at his feet, he was astonished and said, 'Ah! my wife, it is good to keep faith.' 'Yes,' she replied, 'but it is better still that only one man who has lain with me should remain alive.' 7"
Polybius 21.38