In tracing the history of the great ecclesiastical institution known as the papacy, the first figure that stands out with considerable clearness is that of Leo I., or Leo the Great, who was elected bishop of Rome in the year 440. Leo is perhaps the first man who, all things considered, can be called "pope" in the modern sense of the term, although certain of his predecessors in the bishop's seat at the imperial capital had long claimed and exercised a peculiar measure of authority over their fellow bishops throughout the Empire. Almost from the earliest days of Christianity the word _papa_ (pope) seems to have been in common use as an affectionate mode of addressing any bishop, but after the fourth century it came to be applied in a peculiar manner to the bishop of Rome, and in time this was the only usage, so far as western Europe was concerned, which survived. The causes of the special development of the Roman bishopric into the powerful papal office were numerous. Rome's importance as a city, and particularly as the political head of the Mediterranean world, made it natural that her bishop should have something of a special dignity and influence. Throughout western Europe the Roman church was regarded as a model and its bishop was frequently called upon for counsel and advice. Then, when the seat of the imperial government was removed to the East by Constantine, the Roman bishop naturally took up much of the leadership in the West which had been exercised by the emperor, and this added not a little in the way of prestige. On the whole the Roman bishops were moderate, liberal, and sensible in their attitude toward church questions, thereby commending themselves to the practical peoples of the West in a way that other bishops did not always do. The growth of temporal possessions, especially in the way of land, also made the Roman bishops more independent and able to hold their own. And the activity of such men as Leo the Great in warding off the attacks of the German barbarians, and in providing popular leadership in the absence of such leadership on the part of the imperial authorities, was a not unimportant item.