Other critics have explained the prestige of the Papacy as the fruit of successful impostures. For this hypothesis there is little to be said. One or two Popes, not the greatest, have condescended to use forged title-deeds. But the effect of these frauds has been much exaggerated. The most famous of them are the _Donation of Constantine_ and the _False Decretals_. The former, though probably of Roman origin, was little used at Rome, and only served to justify the modest beginnings of the temporal power. The latter are of more importance, and are sometimes regarded as opening an era of new pretensions. In fact they are little more than reiterations and amplifications of very ancient claims. Though frequently quoted by the canon lawyers, they are not indispensable links in the claim of historical proofs and precedents. They are chiefly significant as attesting the general desire of churchmen to find some warrant for a vigorous exercise of the papal prerogative. A primate with real powers was desired, not only by the clergy of the national churches as a bulwark against the brutal oppression of the State, but also by all religious thinkers as a symbol of corporate unity and a guarantee of doctrinal uniformity. No theory can be regarded as supplying a satisfactory explanation of papal authority, unless it explains this general belief in the necessity for a visible Head of the Western Church. In part the necessity was political. Exposed to the common danger of secular tyranny, the national churches looked for safety in federation; and they notified their union in the only way that uneducated laymen could understand, by announcing their subjection to a single spiritual sovereign. But there remained the problem of justifying this act of independence amounting to rebellion. The justification was found in two arguments, the one historical, the other doctrinal; the one based upon the Roman legend of St. Peter, the other on the acknowledged importance of holding fast to right tradition. Each of these arguments calls for some consideration.