The Gallic War of c.284-283 was an obscure conflict which saw the Romans defeat the both the Gallic Senones and an alliance between the Gallic Boii and the Etruscans.
Many of the details of this war are very obscure but we do have an account by Polybius, and more details from other sources.
According to Polybius the war followed ten years of peace with the Gauls, but this ended when a Gallic army besieged the town of Arretium. The Romans sent an army to relieve the town, but they were defeated outside the town and the Praetor Lucius Caecilius was killed. He was replaced by Manius Curius, who sent envoys to the Gauls to negotiate the return of prisoners taken at Arretium. However the Gauls murdered the legates sent to negotiate, a move that infuriated the Romans. They invaded Gallic territory and inflicted a defeat on the Senones (who occupied an area on the Adriatic coast around modern Ancona), driving them out of their country and creating a new city, Sena, in their former lands. This was their first colony in former Gallic lands, and still survives as Senigallia, on the Adriatic coast near Ancona.
This success worried the Boii, who inhabited the area just to the north. The Boii allied with the Etruscans, but their combined army was defeated by the Romans at Lake Vadimon. Most of the Etruscans were killed and only a few of the Boii escaped. In the following year the Etruscans and Boii made one last effort, raising a new army that included ‘mere striplings’. However this army was also defeated and Etruscans and Boii sued for peace.
The fragments of Appian appear to give a different order of events. He starts with the Senones providing mercenaries for the Etruscans, who were already fighting the Romans. The senate sent an embassy, but the Gallic leader Britomaris, whose father had been killed earlier in the same war, killed the ambassadors. The consul Cornelius (P.Cornelius Dolaballa) reacted by invaded the land of the Senones, devastating the area. Britomaris was captured and taken off to be tortured. The remaining Senones attacked the second consul, Domitius (Cn Domitius Calvinus Maximus) and were defeated. The survivors, with no home to return to, killed themselves.
The Periochae of Livy starts with the murder of the envoys by the Senones and then has the defeat of Lucius Caecilius. However no further details are given.
These accounts can be put together in any number of ways. We can be fairly sure that the Romans suffered a defeat in which the Praetor Lucius Caecilius was killed, and that they fought the Gauls and Etruscans. However beyond that we enter into speculation. One possibility is that Britomaris’s father had been killed at Lake Vadimon, which could make the final battle in Appian the same as the battle that follows Lake Vadimon in Polybius. However according to Polybius it was the Boii that fought at Lake Vadimon, not the Senones.
We can be a bit more confident about the date of these events, as the two consuls named were in office in 283 BC, while a Lucius Caecilius Metellus Denter had been consul in 284 BC, and could have been the praetor of 283.
Polybius finishes his account by dating it as happening five years before the defeat of the Gauls at Delphi in 279 BC and three years before Pyrrhus crossed to Italy in 280 BC, which gives us a range of 284-283 BC.
Although this is an obscure and poorly documented war, it was significant in two ways. First, it was the last time that the Senones are recording as fighting against the Romans, thus ending a threat that had existed for a century, since they had been the main Gallic tribe involved in the traumatising battle of the Allia (c.387) and the resulting sack of Rome. Second, it was the first time that the Romans had conquered an area occupied by the Gauls and founded their own settlement in the area.