The expression Ager Gallicus defines the territory of the Senone Gauls after it was devastated and conquered by Rome in 284 BC or 283 BC, either after the Battle of Arretium or the Battle of Lake Vadimon. Destruction of the Ager Gallicus According to Polybius, unspecified Gauls besieged the city of Arretium (Arezzo, in north-eastern Tuscany) and defeated a Roman force which had come to the aid of the city. Their commander, the praetor Lucius Caecilius Metellus Denter died in the battle. This would place the battle in 283 BC because Denter was a consul in 284 BC. Denter was replaced by Manius Curius Dentatus, who sent envoys to negotiate the release of Roman hostages, but they were killed. The Romans marched on Gaul and they were met by the Senones who were defeated in a pitched battle. Polybius used the highly generic term Gaul. He meant Gallia Cisalpina (Gaul this side of the Alp from the Roman geographical viewpoint) which was the name the Romans gave the area of the Gauls of northern Italy (as opposed to Gallia Transalpina, Gaul the other side of the Alps, which referred to what is now southern France). It can be assumed that this clash with the Senones occurred in the ager Gallicus, because Polybius wrote that "the Romans invaded the territory of the Senones, killed most of them and drove the rest out of the country and founded the colony of Sena Gallia (Senigallia)". Polybius did not specify who led this Roman campaign. He also wrote that "[h]ereupon the Boii, seeing the Senones expelled from their territory, and fearing a like fate for themselves and their own land, implored the aid of the Etruscans and marched out in full force. The united armies gave battle to the Romans near Lake Vadimon, and in this battle most of the Etruscans were cut to pieces while only quite a few of the Boii escaped." He also wrote that the next year the Boii and the Etruscans engaged the Romans in battle again and "were utterly defeated and it was only now that their courage at length gave way and that they sent an embassy to sue for terms and made a treaty with the Romans." According to Appian, the Romans sent their ambassadors specifically to the Senones and for a different reason. The Senones had provided mercenaries to forces which had fought against Rome