 In the same period, the Eastern Roman Empire had two palatine field armies (at Constantinople), three regional field armies (in the East, in Thrace, and in Illyricum) and fifteen frontier armies.As Roman troops were spread increasingly thin over its long border, the Empire's territory continued to dwindle in size as the population of the empire declined.Barbarian war bands increasingly began to penetrate the Empire's vulnerable borders, both as settlers and invaders.