Exiled from Rome, and searching for powerful allies to regain their throne, the Tarquins went to the Etruscan king Porsena, who was a relative of theirs. They gave him many reasons why he should help them, appealing first to their close kinship, then arguing that the dignity of the Etruscan race had been insulted when the Romans cast their rulers out, and at last arguing that if Porsena allowed the Romans to cast out their king and rule themselves as a Republic, as they claimed to do, it would inspire other cities to cast off their kinds and become a danger to all who ruled.
At last, Porsena agreed to help restore Rome to the Tarquins' control and called together his army to march on Rome. At the news of the Etruscan army's approach, the Romans gathered within the walled city and barred the gates. Guarded on one side by the city walls and on the other by the River Tiber, they hoped to outlast their attackers, but there was one weak point in the city's defenses: the wooden Sublician Bridge across the Tiber.
Farmers and herders streamed across the bridge from the lands on the other wide of the Tiber, into the city, as the Etruscans approached. But when the lead soldiers of the Etruscans appeared suddenly on the far bank and rushed toward the bridge, even the Roman soldiers set to guard the bridge began to flee. Only one among them, Horatius, stood firm.
As others fled, Horatius stood facing the Etruscans with his spear and shield raised. Seeing his bravery, the other Romans ceased their panic. Two men, Lartius and Herminius, returned to stand with Horatius, while the rest of the guards set to work destroying the bridge so that the Etruscans could not cross into the city.
At first the Etruscan soldiers were shocked to see only three man blocking their way, when up till now the Romans had all fled before them. Then they pushed forward, intending to overwhelm them quickly and cross the bridge into the city. But on the narrow bridge, it was impossible for more than four or five soldiers to approach at a time, and Horatius and his two companions fought them off so fiercely that the surviving Etruscans soon drew back.
On Roman shore, the guards had nearly finished cutting through the bridge's supports, and it began to shake and totter. Horatius sent Lartius and Herminius back to join their fellows, while he himself advanced to the shore and called out that if any among the Etruscan captains dared challenge him, he would fight them in single combat. He was determined to block their way until the bridge was cast down into the river and their way barred.
When no Etruscan champion stepped forward, Horatius taunted them. "No wonder that you have no stomach for this fight, when you come in arms against a free city while you yourselves are slaves. Why do you fight to take from Rome what you have never had yourselves: Freedom from the tyranny of kings."
With that, several of the Etruscans hurled their javelins at him, but Horatius caught them in his shield and stood fast. At that moment, there was a tremendous crash as the bridge fell into the river, and the Etruscans, seeing that Horatius was now the only Roman trapped on their side of the Tiber, gathered their courage and began to close in on him, their spears lowered.
Then Horatius turned to the river and called out, "Tiberinus, mighty river god, accept this warrior and these arms as an offering for the safety of Rome!" And with that, he dived, still armed and carrying carrying his sword, into the deep river.
Many of the Etruscans hurled their javelins after him, but whether through chance or the protection of the river god, none found its mark. Despite the swift current and the weight of his armor, Horatius reached the other bank and drew himself out onto the shore, whether the other Roman guards rushed eagerly to help him.
In the city, Horatius was hailed as a hero of the new Republic, and the Senate voted that when the siege was ended, a statue of him should be erected in the forum. Since Horatius has not, until that time, been a landowner, the Senate also decreed that he should be granted as his own as much land as he could plow around from sunrise to sunset.
But for all this rejoicing, the city was soon surrounded by Porsena's army. The Etruscans crossed the Tiber at a shallow place to the north of Rome. And having encamped both along the river and outside the walls, they waited, confident that the Romans could not hold out long while cut off from their farms outside the city walls.