“Nowruz, literary “New-day”, is the traditional Iranian new year celebration. It has been celebrated in Iran for over two thousand years by all the people regardless of ethnicity, religion, or language. It’s non-ethnic, non-religious characteristic is the precise reason for the fact that it is still prominent outside the political boundaries of modern Iran and is celebrated by people of Central Asia, Caucasus, and many other places in West Asia. It has also been adopted as the official New Year feast of the Baha’i faith, due to their roots in Iran.
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.” As they explain on iranologie.com
Happy Nowruz!! Today the Persian calendar enters the year 1400.