Previous to the eleventh century there had been quarrels between Emperor and Pope. Occasional Popes, such as Nicholas I (858-67), had asserted high prerogatives for the successor of St. Peter, but we have seen that the Church herself taught the co-ordinate and the mutual dependence of the ecclesiastical and secular powers. It was the circumstances of the tenth century which caused the Church to assume a less complacent attitude and, in her efforts to prevent her absorption by the State, to attempt the reduction of the State to a mere department of the Church.