The Etruscan War of 311/10-308 BC was a short conflict between Rome and some of the inland Etruscan cities that for a brief period saw Rome facing a war on two fronts, against the Etruscans to the north and the Samnites to the south.
The Etruscan War falls in a period in which the traditional Roman chronology is probably incorrect. In this chronology the war took place in 311 to 308 BC, but that chronology includes a 'dictator year' in 309 BC, in which no consuls were recorded. Neither Livy nor Diodorus Siculus mention this year, and it was probably a later invention inserted in the list of consuls in an attempt to reconcile two different historical traditions.
Neither Livy nor Diodorus give any reason for the outbreak of the war. Livy reports that the Etruscans began to prepare for war in 312/11, and that the Romans responded by appointing C. Junius Bubulcus as dictator. He raised a new army, but was unwilling to be responsible for starting the war, and so the hostilities were delayed until the following year.
The war began with an Etruscan attack on the city of Sutrium, a key Romen border city. The Romans sent the consul Q. Aemilius Barbula to lift the siege, but although he won a victory over the Etruscan army the Romans suffered heavy losses themselves, and were unable to force the Etruscans away.
At the start of the next year the consul Q. Fabius Maximus Rullianus took command of the Etruscan War. He too was credited with a victory over the Etruscans at Sutrium, but the siege continued. One of Fabius's officers, possibly his brother, suggested crossing the great Ciminian forest, then a trackless wilderness that acted as a border between Etruria and Rome. This officer crossed the forest with a single servant, eventually reaching Camerinum, where he arranged an alliance. This convinced Fabius to risk crossing the forest, and after a single days marching the Romans had reached a position on the Ciminian hills, overlooking the Etruscan heartland.
Livy and Diodorus Siculus provide similar accounts of the campaign on the far side of the forest. Diodorus reports two Roman victories, the first at an unnamed location, and the second close to Perusia. After this victory he agreed truces with the people of Arretium, Cortona and Perusia.
In Livy Fabius defeated a force made up of local peasantry, probably the first battle records by Diodorus. Livy then records a second battle, which in his main account takes place back at Sutrium, but that he admits might have been fought near Perusia. After this victory he arranged a truce with Arretium, Cortona and Perusia.
Diodorus's account ends at this point, but Livy goes on to record a third battle, at Lake Vadimo in the upper Tiber valley. This saw the Romans defeated the largest Etruscan army yet, and break the power of the remaining hostile cities.
In 308 the consul P. Decius Mus was allocated the Etruscan War. He agreed a new 40 year truce with the coastal city of Tarquinii and then campaigned against Volsinii, in the Tiber valley. After the Romans captured and destroyed a number of Volsinii strong points the Etruscan League sued for peace, and asked for a peace treaty. Decius didn't agree to this, but he did agree to a one year truce.
This ended the Etruscan phase of the war, but now the Umbrians rose in arms, perhaps realising that they would be the Roman's next target. While Decius moved back into the territory of Pupinia to block the Umbrian's route towards Rome, his colleague Q. Fabius Maximus Rullianus made a forced march from Samnium, and defeated the Umbrians at Mevania.
This ended the war and left the Romans free to concentrate on defeating the Samnites. At the same time they agreed an alliance with the southern Umbrian city of Ocriculum, and on 303 BC, the year after the end of the Second Samnite War, they returned to Umbria.