A guardian angel is a spirit who is believed to protect and to guide a particular person. The concept of tutelary angels and their hierarchy was extensively developed in Christianity in the 5th century by Pseudo-Dionysius the Areopagite. The theology of angels, and tutelary spirits, has undergone many refinements since the 400's, and contemporary orthodox belief in both the eastern and western churches is that guardian angels protect the body and present prayers to God, protecting whichever person God assigns them to. The Roman Catholic Church calendar of saints includes a memorial for guardian angels on October 2.