Pythagoras and Pythagoreanism have a different position in the ancient philosophy tradition. The reason for this is the eclectical structure of Pythagoreanism which has syncretized from Orphism, Indian and Egyptian religions with philosophy. Orphism of these religions is especially important for affecting Pythagoreanism the most and giving to the ancient Greek religion a mystical content. Orphism which is a mystery cult is based on Orpheus, the poet, who sometimes is identified with Pythagoras in philosophy and the history of religions. Orpheus, was attributed divine character by virtue of his beautiful voice and hymns in the ancient history, has brought many religious and philosophic elements such as reincarnation and unity with God to the Greek religion. The way of life and creeds of Orphism based on asceticism and wisdom, first affected Italian philosophy starting from Pythagoras and, later influenced both philosophy and the other religions such as Judaism and Christianity through Plato. The reason for this was the Orphism's stronger theological structure than the Greek religion had. Thus, philosophy, the Miletus philosophers tried to purify from the Homeric religion, has regained some spirituality through Orphism and Pythagoras. Pythagoras, a philosopher and a religious leader, accepted students to his philosophy school by initiation in Crotone. In this way, Pythagoreanism gained the quality of both a school of philosophy and a community of mystery. In this school, Pythagoras constituted a strong natural philosophy based on the idea of arkhe consisting of numbers, and the system of mathematics and music. At the same time, for he was a religious leader, Pythagoras used his school both to teach philosophy and to celebrate the teletaic mystery rituals of Orphism. According to the Pythagoreans, as a master, Pythagoras has united with the spirit of Dionysos and has privileged to rise to the World-Soul of God. Due to this union, it has been believed that Pythagoras received revelations from Dionysos and knew the secrets of God's spirit. Similarly, Pythagoras' students of philosophy also joined these rituals. They, on the one hand, witnessed to the divine union of Pythagoras, on the other hand, experienced the communication with the subordinate gods, called daemons, allied to Dionysos. Through these mystical rituals in Pythagorean school, it was believed that the philosophical knowledge was not only a reasoning, but also a divine wisdom obtained from the divine word. Therefore, Pythagoreanism accepted that philosophy is from God and it is a way of life which rises the human to the divine level. According to Pythagoras philosophy, thinking about God is equal to dealing with natural philosophy. Because Pythagoreanism, that has a pantheistic belief in God, has acknowledged God and nature as the same. Additionally, the natural philosophy of the school was established on the Monad idea which has been accepted as the World-Soul. For Pythagoreanism, Monad is not a number, but it is the ONE as the source of all numbers and a theological principle. The ONE, which symbolizes God and the cosmic unity, brings into existence the life by limiting the chaos caused by the TWO. Similarly, the TWO, not a number but a principle, has been used in a positive sense in Anaximander and was called apeiron, meant "infiniteness". But, for Pythagoras, infiniteness was a negative circumstance. For this reason, the TWO/Apeiron has been accepted as a female being which corresponds to limitless absence and evil. By Monad's confinement the Apeiron had been passed into the cosmos, the cosmic harmony had been balanced and a spheric being had emerged. This is "unity" which corresponds with both the World Soul Monad and the nature in the Pythagorean philosophy. This study will discuss the notion of Monad which is known as the World-Soul and God in Pythagorean philosophy, from a perspective of the history of religions. In this context, the sources and knowledge of history of philosophy will be used by methods of the history of religions. Starting from Orphism, Monad will be discussed within similar mythical elements. Thus, the origin of the Pythagorean philosophy in ancient religions will be determined and the theological infrastructure will be shown.