From this day forward, Light triumphs as the days grow longer and gives more light.When Mithraism spread to ancient civilised world from Iran, Dec 21st was celebrated as Mithra’s birthday. But in the 4th century AD because of some errors in counting the Leap Year, the birthday of Mithra shifted to Dec 25th. Until that time the birthday of Jesus Christ was celebrated on Jan 6th. But the religion of most of the Romans and the people of many of the European countries was still Mithraism.When Christianity spread, the priests could not stop the practice of celebrating Mithra’s birthday on Dec 25th, so they declared this day as Jesus’s birthday which is still so.In ancient Persia, Yalda festivities were symbolized by the evergreen tree. Young girls wrapped their wishes in silk cloth and hung them on the tree. Eventually, it became a custom to place presents/gifts under the evergreen tree. As late as the 18th century a German learnt of the Yalda tree and created what we now know as the Christmas tree.For decades the entire Iranian nation, particularly Zarthushtis, celebrate Yalda more as the night of the rebirth of the “Sun” than connect it with the birth of Jesus. Yalda also known as Shab-e Cheleh in Persian is celebrated on the eve of the first day of the winter (December 21) in the Iranian calendar, which falls on the Winter Solstice and forty days before the next major Iranian festival "Jashn-e Sadeh (fire festival)". As the longest night of the year, the Eve of Yalda (Shab-e Yalda) is also a turning point, after which the days grow longer. It symbolised the triumph of Light and Goodness over the powers of Darkness. Yalda celebration has great significance in the Iranian calendar. It is the eve of the birth of Mithra, the Sun God, who symbolised light, goodness and strength on earth. Shab-e Yalda is a time of joy. The festival was considered pone of the most important celebrations in ancient Iran and continues to be celebrated to this day, for a period of more than 5000 years. Yalda (yaldā) is a Syriac word meaning birth (NPer. tavvalod and milād are from the same origin). In 3rd century CE, Mithra-worshippers adopted and used the term 'yalda' specifically with reference to the birth of Mithra.