Sextus Tarquinius was the third and youngest son of the last king of Rome, Lucius Tarquinius Superbus (Tarquin the Proud). According to Roman tradition, his rape of Lucretia was the precipitating event in the overthrow of the monarchy and the establishment of the Roman Republic.
Rape of Lucretia 
Tarquinius was besieging Ardea, a city of the Rutulians. The place could not be taken by force, and the Roman army lay encamped beneath the walls. Here as the king's sons, and their cousin, Tarquinius Collatinus, the son of Egerius, were feasting together, a dispute arose about the virtue of their wives. As nothing was happening in the field, they mounted their horses to visit their homes by surprise. They first went to Rome, where they surprised the king's daughters at a splendid banquet. They then hastened to Collatia, and there, though it was late in the night, they found Lucretia, the wife of Collatinus, spinning amid her handmaids. The beauty and virtue of Lucretia had fired the evil passions of Sextus. A few days later he returned to Collatia, where he was hospitably received by Lucretia as her husband's kinsman. In the dead of night he entered the chamber with a drawn sword ; by threatening to lay a slave with his throat cut beside her, whom he would pretend to have killed in order to avenge her husband's honour, he forced her to yield to his wishes.
Soon after, Lucretia sent a message to both her husband and her father, Spurius Lucretius Tricipitinus, telling them everything. She then killed herself. The revolt that followed, led by her husband's friend Lucius Junius Brutus, brought to an end the kingship of Tarquin the Proud and brought about the beginning of the Roman Republic, Brutus becoming the first consul together with Collatinus. Sextus Tarquinius fled to Gabii, to seek to make himself king, but he was killed in revenge for his past actions.
Cultural references 
Lucretia and Tarquinius have been the subject of many paintings, including those by great artists.
The story of Lucretia's rape is the subject of William Shakespeare's narrative poem The Rape of Lucrece, a work as long as many full-length plays, taking about two hours to recite. It has sometimes been performed as readers' theatre. Shakespeare alludes to Tarquinius in his plays as well. In Cymbeline (Act 2, Scene 2), Iachimo has slipped into the sleeping Imogen's bedchamber, and compares himself to Tarquin:
... Our Tarquin thus
Did softly press the rushes, ere he waken'd
The chastity he wounded … .
With Tarquin's ravishing strides, towards his design moves like a ghost.
… Shall Rome stand under one man's awe?
What, Rome? My ancestors did from the streets of Rome the Tarquin drive, when he was call'd a king.
Sextus Tarquinius is present with the Etruscan army in Thomas Babington Macaulay's Lays of Ancient Rome, when Lars Porsena, King of Clusium, attempts to restore the Tarquin dynasty to the Roman throne:
By the right wheel rode Mamilius, prince of the Latian name,
And by the left false Sextus, who wrought the deed of shame.
But when the face of Sextus was seen among the foes,
A yell that rent the firmament from all the town arose.
On the house-tops was no woman but spat toward him and hissed,
No child but screamed out curses, and shook its little first.