The next most constant source of trouble was the pernicious influence of the Philosophers--a set of men who pretended to be seekers after wisdom, and distinguished themselves from the vulgar by a certain style of dress. Puffed up as they were with their own knowledge, nothing irritated their pride so much as that men of the despised Christian class should presume to dispute their doctrines and teach that profane philosophy was naught, since man could not be made perfect by human wisdom, but only by the testimony of Christ who was crucified. Among the Christians, too, a special order of men whom we call Apologists, and among whom we count Justin, Tertullian, Tatian, Arnobius, Minutius Felix, Origen, Aristides, Quadratus, Athenagoras, and Miltiades the chief, exposed in their eloquent writings the vanity, contradictions, and vices of their opponents, succeeding sometimes in silencing false accusations, and even in arresting the course of persecution. Their apologies and memorials form one of the most instructive branches of early Christian literature, and are a considerable compensation for the loss of so many Acts of martyrs and other venerable documents destroyed by the pagans or which have otherwise perished. The third great cause of persecution was found (to use a comparatively modern word) in the Erastianism of the Roman Empire. The emperor was, by right of the purple, high-pontiff, and no religion was recognized that did not profess its existence and authority dependent upon the state. Naturally, a religion whose followers would reply to every iniquitous command, “We ought to obey God rather than men,” could expect no mercy, but only continual war.