Peter Brown, a known authority on Mediterranean civilisation in late antiquity, traces the growing power of early Christian bishops as they wrested influence from the philosophers who had traditionally advised the rulers of Graeco-Roman society. In the new "Christian empire", the ancient bonds of citizen to citizen and of each city to its benefactors were replaced by a common loyalty to a distant, Christian autocrat. This transformation of the Roman Empire from an ancient to a medieval society, Brown argues, is among the most far-reaching consequences of the rise of Christianity. In the last centuries of the Roman Empire, the power of the emperors depended on collaboration with the local elites. The shared ideals of Graeco-Roman culture ("paideia"), which were inculcated among the elite by their education, acted as unwritten constitution. The philosophers, as representives of this cultural tradition and as critics and advisors of the powerful, upheld the ideals of just rule and prevented the abuses of power.