An incident that occurred during the reign of Tarquinius Superbus about 400BC that effectively ensured the end of the Roman Monarchy. Tarquinius Superbus' son, Sextus, was the orchestrator of the vile deed, and it started with a simple joke between him and his friends. They were away from Rome engaging the city of Ardea in siege, and they wondered if their wives would sleep around/get drunk/party now that the "cat was away", so's to speak. The Roman concept of a "good woman" was rather chauvinist, and so imagining that one's wife would try to cheer herself up by eating out with her lady friends was not considered a good one.
Anyway, they decided to bet amongst themselves as to whose wife would be the most demure and well-behaved while they were away, and after putting money on it, all rode off home to check on their wives. It was the wife of Colatinus, Lucretia, who was in fact the most chaste of all, and sat at home knitting.
Collatinus won the bet, and everyone went home, but it was not the end for Lucretia. Her purity probably inspired Sextus to rape her, to deflower her if you will. However, he was cunning, and did not rape her at this point, with her husband in the house. He returned alone a few days later and asked to be put up for the night as a friend of her husband. While she was asleep, he crept out of the guest bedroom, and threatened her with a sword. Though she refused to submit at first, preferring death, he told her that he would kill her, then kill a slave and finally lay the two bodies together, so it would look as though she had been killed mid-coitus with said slave (a terrible dishonour). Finally, with this horrible threat hanging over her, she agreed.
After Sextus had ridden away on his horse, Lucretia sent for her father and husband, each with a friend, to see her. Colatinus brought his friend Brutus, Tarquin's nephew (and a man with his own grudge against Tarquin). Arriving a little later, the four men were shocked to find Lucretia in tears, and she explained what had happened. She explained that she had been debased, and that she would not let any unchaste woman cite her as an example of someone who had lost their chastity and gone on living, and so then, drawing a sword from her dress, she stabbed herself, to the horror of the people around her.
Brutus (ancestor of the more famous Brutus who killed Caesar), whose father had been killed by Tarquin, used this opportunity to stir up mobs in Rome, and led the furious people to drive Tarquin into exile and set up the Roman Republic.