h East and West. The
infallibility of the episcopate guarantees the infallibility of a
general council in which not the laity and not the clergy in general,
but the bishops as successors of the apostles, speak officially and
collectively.

Another organized expression of the unity of the Church was found in the
metropolitan system, or the grouping of the churches of a province under
a single head, who was usually the bishop of the capital city, and was
known as the metropolitan bishop. The Church thus followed in its
organization the political divisions of the Empire (cf. for instance
canon 12of the council of Chalcedon, which forbids more than one
metropolitan see in a province; also canon 17 of the same council: "And
if any city has been or shall hereafter be newly erected by imperial
authority, let the arrangement of ecclesiastical parishes follow the
political and municipal forms"). These metropolitan bishops were common
in the East before the end of the 3rd century, and the general existence
of the organization was taken for granted by the council of Nicaea (see
canons 4,6,7). In the West, on the other hand, the development was much
slower.

Meanwhile the tendency which gave rise to the metropolitan system
resulted in the grouping together of the churches of a number of
contiguous provinces under the headship of the bishop of the most
important city of the district, as, for instance, Antioch, Ephesus,
Alexandria, Rome, Milan, Carthage, Arles. In canon 6 of the council of
Nicaea the jurisdiction of the bishops of Alexandria, Rome and Antioch
over a number of provinces is recognized. At the council of
Constantinople (381) the bishop of Constantinople or New Rome was ranked
next after the bishop of Rome (canon 3), and at the council of Chalcedon
(451) he was given authority over the churches of the political dioceses
of Pontus, Asia and Thrace (canon 28). To the bishops of Rome,
Constantinople, Antioch and Alexandria was added at the council of
Chalcedon (session 7) the bishop of Jerusalem, the mother church of
Christendom, and the bishops thus recognized as possessing supreme
jurisdiction were finally known as patriarchs.

Meanwhile the Roman episcopate developed into the papacy, which claimed
supremacy over the entire Christian Church, and actually exercised it
increasingly in the West from the 5th century on. This development was
forwarded by Augustine, who in his famous work _De civitate Dei_
identified the Ch