Medieval Christendom was divided into two parts. The Christians of eastern Europe were under the leadership of the patriarch of Constantinople (modern day Istanbul, in Turkey). Those in western Europe (which this article mainly deals with) were under the leadership of the bishop of Rome, commonly called the pope (papa, or “father”). These two branches gradually adopted different practices – for example the Western church came to ban clerical marriage, while the Eastern church did not – and there was growing friction between the two. Eventually, with the pope claiming seniority over the patriarch, and vice versa, both sides excommunicated each other in 1054. This began a schism which would last throughout the Middle Ages and beyond.
