Ancient Iranian religion was strongly connected. Beginning in the early 10th-century BC, the ancient Iranian religion was gradually displaced by Zoroastrianism, which contains many essential aspects of its predecessor. The sources on ancient Iranian religion, though limited, consist of textual and material sources. The textual sources are both Iranian and non-Iranian. An important Iranian source is the Avesta, which are Zoroastrian sacred scriptures made in the Avestan. This is considered the principal source of knowledge on ancient Iranian religions. It is a collection of several texts that seems to have been over a large span of time by a variety of authors. These
Definition of religion definitions are to be found in the writings of, for example, Frederick Ferré who defined religion as "one's way of valuing most comprehensively and intensively". Similarly, for the theologian Paul Tillich, faith is "the state of being ultimately concerned", which "is itself religion. Religion is the substance, the ground, and the depth of man's spiritual life." When religion is seen in terms of sacred, divine, intensive valuing, or ultimate concern, then it is possible to understand why scientific findings and philosophical criticisms (e.g., those made by Richard Dawkins) do not necessarily disturb its adherents. A number of scholars have pointed