Derived from the Sanskrit language, the word ‘Songkran’ means “to pass or to move into”. In this context, the meaning implies to the passing and the moving of the sun, the moon and the other planets into one of the zodiacal orbits. And the Grand Songkran Festival which falls in Aries indicates the new era of the Thai New Year. Owing to the ancient Indian belief, the Grand Songkran Festival is most appropriate to be the Thai New Year due to the timing of the best season which is known as the spring of India which comes right after the cold season of winter. Also, there are other aspects supporting this belief such as blooming flowers, the fresh atmosphere of nature and the livelihood of all living creatures.
With the great influence from the Indians, the Songkran Festival portrays the typical ways of life of the Thais which involve the agricultural aspects. Free from their regular routine work, the Thai citizens will find time to perform their annual rites of showing respect to their ancestors. The highlight of the festival will include the younger Thais paying respect to their elders by sprinkling their hands with scented water. And in order to welcome the New Year, the celebration will include the delightful colorful local entertainment, which in fact, suitably unites the mutual relationship between members of the family, society, nature and the surroundings. Therefore, this Songkran Festival has proved to be the most important and grandest festival of the year. Moreover, our neighbouring countries such as Myanmar, Cambodia and Lao PDR. have also organised this type of festival.
During the Sukhothai period, the Songkran Festival was practised both in the royal court palace and among the ordinary citizens. However, the size of the celebration was not as elaborate as of today. Back in those days, civil servants and other government officials would pay homage to the king, and would drink the oath of allegiance to the king or the government, while the king would provide an annual salary to all officials. Later on in the Ayutthaya period, the festival was expanded by including the bathing of the Buddha image. Also, the festivities would include the forming of sand pagodas and entertaining celebrations. In the Rattanakosin period, the rituals have been conducted in a similar pattern as those during the Ayutthaya period.
source: http://songkran.tourismthailand.org/history.php