Nowruz is commonly perceived as the most “Iranian” of all celebrations, emphasising an Aryan/Indo-Iranian root for the celebration. However, the lack of any mention of Nowruz or the traditional, well-known celebrations associated with it in Achaemenid inscriptions as well as the oldest parts of the Avesta, the Old Iranian hymns of Zoroastrianism, can point to the non-Iranian roots of the celebration.
We know that the Sumerian and Babylonian calendars of the Mesopotamia were based on the changing of the seasons. The sedentary agriculture of Mesopotamia that served as the backbone of Babylonian economy greatly depended on the changing of the seasons and the amount of yearly downpour. Subsequently, the beginning of the spring mattered greatly in Mesopotamia and was celebrated accordingly. There also existed an annual ritual in Babylonia when at the beginning of the spring the king was required to make a journey to the temple of Marduk and receive the regal signs from the god and give royal protection to the great god of Babylon. The yearly renewal of this mutual support seems to symbolize the renewal of life marked by the beginning of the spring. We have decisive records of the adoption of this ritual by the Iranians when Cyrus the Great invaded Babylon and appointed his son, Cambyses, as his deputy there.
On the other hand, the life style of Iranian tribes prior to their settlement in Iran was nomadic and greatly depended on cattle raising instead of sedentary agriculture, thus devoid of the need to keep exact track of seasonal change. Their homeland, in the central Asian steppes, possessed either very cold winters or scorching summers and the arrival of spring seldom had the same effect as it does on the more temperate lands to the south.
As a result, it is possible to conclude that the original roots of Nowruz laid in the Mesopotamian celebration of the arrival of spring and was later adopted by settled Iranian tribes, probably as early as the reign of the first Achaemenid emperor. It should be pointed out that if we accept this theory of adoption, we should not forget the certain Iranian characteristics that shaped this celebration into a distinctly Iranian custom.
Among the most prominent of these characteristics is the adaptation of Iranian world-view into the rituals of Nowruz. Although we have evidence that in the mid years of the Sasanian period, due to the neglect in maintaining the calendar, Nowruz was sometimes celebrated in the early summer or mid-winter, we should remember that the original place of Nowruz was always at the beginning of the spring. Different branches of Iranian Gnosticism that were popular in the late Sasanian and early Islamic era, most prominently displayed in Manichaeism, saw the world as a place of battle between the forces of good and evil. Manichaeism, and its Iranian roots in the religion of the Magi, defined darkness and cold as the signs of evil and lightness as the force of rightness. In fact, the most obvious characteristic of the Manichean deities is their extraction of light, a fact that later even influenced Christianity and its concept of halo. Thus, it was easy for most people to associate winter with forces of evil and see spring as the rebirth of light. Subsequently Nowruz was seen as the triumph of light over dark and the beginning of the rejuvenation of the world.
__________________ Source: http://www.iranologie.com/history/nowruz-hist.html
