We have already seen how marvelously the Christian communities founded by the apostles and their fellow-missionaries multiplied until, by the middle of the third century, writers like Cyprian came to conceive of a "Catholic," or all-embracing, Church. We have seen how Constantine first made Christianity legal, and how his successors worked in the interest of the new religion; how carefully the Theodosian Code safeguarded the Church and the Christian clergy, and how harshly those were treated who ventured to hold another view of Christianity from that sanctioned by the government.[25] We must now follow this most powerful and permanent of all the institutions of the later Roman Empire into the Middle Ages. We must stop a moment to consider the sources of its power, and then see how the Western, or Latin, portion of Christendom fell apart from the Eastern, or Greek, region and came to form a separate institution under the longest and mightiest line of rulers that the world has ever seen, the Roman bishops. We shall see how a peculiar class of Christians, the monks, developed; how they joined hands with the clergy; how the monks and the clergy met the barbarians, subdued and civilized them, and then ruled them for centuries. [Sidenote: Sources of the Church's power.] The tremendous power of the Church in the Middle Ages was due, we may be sure, to the way in which it adapted itself to the ideas and needs of the time; for no institution can flourish unless it meets the wants of those who live under it. [Sidenote: Contrast between pagan and Christian ideas.] One great source of the Church's strength lay in the general fear of death and judgment to come, which Christianity had brought with it. The Greeks and Romans of the classical period thought of the next life, when they thought of it at all, as a very uninteresting existence compared with that on this earth. One who committed some signal crime might suffer for it after death with pains similar to those of the hell in which the Christians believed. But the great part of humanity were supposed to lead in the next world a shadowy existence, neither sad nor glad. Religion, even to the devout pagan, was mainly an affair of this life; the gods were to be propitiated with a view to present happiness and success. Since no satisfaction could be expected in the next life, it was naturally deemed wise to make the most of this one. The possibility of pleasure ends--so the poet Horace urges--when we join the shades below, as we all must do soon. Let us, therefore, take advantage of every harmless pleasure and improve our brief opportunity to enjoy the good things of earth. We should, however, be reasonable and temperate, avoiding all excess, for that endangers happiness. Above all, we should not worry uselessly about the future, which is in the hands of the gods and beyond our control. Such were the convictions of the majority of thoughtful pagans.