A cathedral is a Christian church that serves as the bishop's residence. Cathedrals are the principal church of a diocese since they are the seat of a bishop. Cathedrals are only found in Christian religions that have bishops. However, some dioceses have additional churches that are larger than the cathedral. These churches may be designated as cathedrals to distinguish them from other large churches in the diocese. All over the world there are many beautiful cathedrals. The first cathedral was built around AD 350 on the site where St. Peter lived. It was made of wood and burned down several years later. The second one was built about 20 years later and it used stones taken from Solomon's Temple to build it. This second cathedral also burned down several years later. The third one was built more than 1000 years after the first two cathedrals. It used stone donated by different people who wanted to show their support for Christianity. Today this third cathedral is called "The Cathedral of Cologne" because it has been the home church for seven German kings.