Comparison of Roman and Celtic Empires 257-357 (Abrittus)

In 257, amidst the chaos of civil war, Frankish invasions, religious conflicts and Sassanid attacks, the Imperium Romanum Galliarum seceded from Rome. As in OTL, it comprised Baetica, Lusitania, Hispania Tarraconensis, Aquitania, Gallia Lugdunensis, Gallia Belgica, Germania Inferior, Germania Superior, Britannia Inferior and Britannia Superior.

In this timeline, a revolution turned the rest of the Imperium Romanum into the Second Roman Republic, while the breakaway Imperium Romanum Galliarum only underwent minor changes of social, economic and political structures in the first one hundred years of its existence. This timespan thus offers the opportunity of an interesting synchronous comparison between the order of Late Antiquity as we know it in OTL and the social, economic and political model of the Second Roman Republic. It also makes analyses of the mutual influences of both competing systems possible. While such a comparison alone cannot explain the Celtic Revolution of the 360s, which was also owed to the turmoil caused by the (early) arrival of the Huns, it can shed some light on some factors which have contributed to it.

Political Structures
After the revolution, the Second Roman Republic was a federal democracy (for more detail, see Roman constitution of 263). Except for a small minority of "peregrini" (temporary refugees, foreign merchants etc.), everyone who lived in the Roman Empire was a citizen with equal voting rights. Most decisions were taken on a relatively local level (a "civitas" usually compt