The Oath of the Horatti by Jacques-Louis David

An argument between the peoples of Rome and Alba threatened to lead to war and so it was decided that each side (the Horatti and the Currati) would send three men to fight for their city. After the batttle only one man remained a live, Horatius. He discovered that his sister had been betrothed to one of the enemy Curatii. In revenge he slew his sister and was found guilty of murder but manageed to get a reprieve from the death sentence. In art the 3 brothers are usually shown swearing a sacrificial oath in front of thier father.

Source:- The History of Painting - Sr Wendy Beckett