Senonia (Kingdom of Brennos)

The Kingdom of Senonia (388-359 BCE), (not to be confused with the client state of Senonia as part of the Gallic Empire), was a short-lived, tribal organized, Gallic kingdom located in Central Italy. It was founded by the Gallic war-leader Brennos, after he sacked and subdued most Rasennan cities, taking in massive amounts of loot. After the Rasennans rose up in 360 BCE, Brennos was killed a year later and his kingdom collapsed. Most Senones retreated to northern Italy, where they continued living as a tribe.

History
The Kingdom of Senonia was founded in 388 BCE by the Gallic war-leader Brennos, after he sacked and subdued most Rasennan cities, taking in massive amounts of loot. It controlled most of the Rasennan territory, stretching from north of the city of Sena, all the way to Veia (OTL Veii).

After the Rasennans rose up in 360 BCE, many Italians joined the revolt. The Gallic army, and the Italian army, clashed together near Veia, and the unorganized Gauls were defeated. The Rasennans and their Italian allies managed to push the Celts into retreat, and the former routed them. The already old Brennos was killed a year later and his kingdom collapsed. Most Senones retreated to northern Italy, where they continued living as a tribe.

Source
https://en.wikipedia.org/wiki/Senones

https://en.wikipedia.org/wiki/Brennus_(leader_of_the_Senones)