During this period, the Romans, while maintaining the levy system, adopted the Samnite manipular organisation for their legions and also bound all the other peninsular Italian states into a permanent military alliance (see "Socii"). The latter were required to supply (collectively) roughly the same number of troops to joint forces as the Romans to serve under Roman command. Legions in this phase were always accompanied on campaign by the same number of allied "alae" (Roman non-citizen auxiliaries), units of roughly the same size as legions.