And there is yet another cause of the decay of communal institutions, which stands higher and lies deeper than all the above. The history of the medieval cities offers one of the most striking illustrations of the power of ideas and principles upon the destinies of mankind, and of the quite opposed results which are obtained when a deep modification of leading ideas has taken place. Self-reliance and federalism, the sovereignty of each group, and the construction of the political body from the simple to the composite, were the leading ideas in the eleventh century. But since that time the conceptions had entirely changed. The students of Roman law and the prelates of the Church, closely bound together since the time of Innocent the Third, had succeeded in paralyzing the idea--the antique Greek idea--which presided at the foundation of the cities. For two or three hundred years they taught from the pulpit, the University chair, and the judges' bench, that salvation must be sought for in a strongly-centralized State, placed under a semi-divine authority;(41) that one man can and must be the saviour of society, and that in the name of public salvation he can commit any violence: burn men and women at the stake, make them perish under indescribable tortures, plunge whole provinces into the most abject misery. Nor did they fail to give object lessons to this effect on a grand scale, and with an unheard-of cruelty, wherever the king's sword and the Church's fire, or both at once, could reach. By these teachings and examples, continually repeated and enforced upon public attention, the very minds of the citizens had been shaped into a new mould. They began to find no authority too extensive, no killing by degrees too cruel, once it was "for public safety." And, with this new direction of mind and this new belief in one man's power, the old federalist principle faded away, and the very creative genius of the masses died out. The Roman idea was victorious, and in such circumstances the centralized State had in the cities a ready prey.