In 509 BC, the Roman monarchy was overthrown and the Roman Republic was established with the election of the first consuls. The deposed king, Lucius Tarquinius Superbus, whose family originated from Tarquinii in Etruria, garnered the support of the Etruscan cities of Veii and Tarquinii, recalling to the former their regular losses of war and of land to the Roman state, and to the latter his family ties.^{[citation needed]}

The armies of the two cities followed Tarquin to battle, and the Roman consuls led the Roman army to meet them, with Publius Valerius commanding the Roman infantry and Lucius Junius Brutus the equites. Similarly, the king commanded the Etruscan infantry, and his son Aruns had command of the cavalry.^{[citation needed]}

The cavalry first joined battle and Aruns, having spied from afar the lictors, and thereby recognising the presence of a consul, soon saw that Brutus was in command of the cavalry. The two men, who were cousins, charged each other, and speared each other to death. The infantry also soon joined the battle, the result being in doubt for some time. The right wing of each army was victorious, the army of Tarquinii forcing back the Romans, and the Veientes being routed. However the Etruscan forces eventually fled the field, the Romans claiming the victory.^[1] According to Plutarch the battle was said to have been fought on the last day of February.

On the night after the battle, Livy reports that a voice believed to be the spirit of Silvanus was heard to come from the nearby forest, saying "more of the Etrurians by one had fallen in the battle; that the Roman was victorious in the war".^[2]

The consul Valerius collected the spoils of the routed Etruscans. He returned to Rome to celebrate a triumph which, according to the Fasti Triumphales, took place on 1 March 509 BC. The funeral of Brutus was carried out by Valerius with great magnificence.^[2][3]

Livy writes that later in 509 BC Valerius returned to fight the Veientes. It is unclear whether this was continuing from the Battle of Silva Arsia, or was some fresh dispute. It is also unclear what happened in this dispute.^[4]