“This is quite an important aspect of Barbarian Invasion, and you should read the the more detailed section on Hordes later even if you normally ignore game manuals. It’s a pity if you ignore game manuals, as writers have fought and died to bring you these words. Honest.”
From, Total War: Rome: Barbarian Invasions manual, possibly by Mike Brunton. Presumably the same Mike Brunton that used to write Warhammer stuff.