Magha puja day is considered one of the most important Buddhist celebrations. It refers to the worship that takes place on the full moon of the third lunar month (about the last week of February or early March) to commemorate the day on which Lord Buddha recited the "Ovadha Patimokkha" (the Fundamental Teaching) to his disciples.
This day marks the great four events that took place during Lord Buddha's lifetime, namely; The time of the full moon in the third lunar month, 1,250 Buddhist monks from differents places came to pay homage to the Lord Buddha at Veluwan Temple in Rajgaha City of Magaha State, without any appointment, all of them were Arahants (enlightened monks) who had attained the Apinyas (Six Higher Knowledges), all of them had been individually ordained by Lord Buddha himself (Ehi Bhikkhu).
Later, the Magha Puja ceremony was widely accepted and performed throughout the country. The evening of that day, Lord Buddha gave the assembly a discourse "Ovadha Patimokkha", laying down the principles of His Teachings to be followed by all Buddhists, summarized into three acts, i.e. to do good, to abstain from bad action and to purify the mind.
Magha Puja Day was never celebrated in Thai kingdom. King Chulalongkorn (Rama V) explained that "..the Magha Puja was never performed, the ceremony has just been practised during the reign of King Mongkrut (Rama IV) of the Chakri Dynasty".
Having realized the importance of this day, King Rama IV ordered the royal Magha Puja Ceremony to be performed in the Emerald Buddha Temple in 1851 and to celebrate it yearly.
Later the ceremony was widely accepted and performed throughout the kingdom. It was declared to be a public holiday back then so everybody could go to the temple to merit and perform other religious activities in the morning and to take part in the candlelit procession or "Wien Tien" in the evening.