Mela Maghi, held at the holy city of Sri Muktsar Sahib each year in January, or the month of Magh according to Nanakshahi calendar is one of the most important melas (fairs) of India and the most important of all religiously significant gatherings of the Sikhs.
Guru Amar Das Ji chose Maghi as one of the three festivals to be celebrated by Sikhs (the others being Baisakhi and Diwali) 
After the battle of Muktsar took place in 1705, Maghi became to be associated with the forty Sikhs and the battle of Muktsar. Although the battle took place in December 1705, the Maghi festival, already being celebrated by Sikhs, was chosen to commemorate the battle, especially since the festival is so near to the date of the battle.
The Maghi fair is held to honour the memory of the forty Sikh warriors killed during the Battle of Muktsar in 1705. Muktsar, originally called Khidrana, was named as Muktsar ("the pool of liberation") following the battle. These forty Sikhs, led by their leader Mahan Singh, had formally deserted Sri Guru Gobind Singh in the need of hour, and signed a written memorandum to the effect. When Mai Bhago, a valiant and upright lady, heard of this cowardly act, she scolded the Singh's and inspired them refresh with spirit of bravery for which Sikhs are known. Hence the unit went back and joined the Guru who was already engaged in action at Khidrana. All forty of them attained martyrdom. The memorandum (bedawa) was torn-down by the Guru himself just before Mahan Singh died.
People gather from all over Punjab, even other parts of India to join the festival which is in fact spread over many days. Merchants display their wares for sale, which include from trinkets to high-end electronics, the weapons Nihangs bear and especially agricultural machinery (since most around are farmers). The country's biggest circuses, Apollo and Gemini, are there as a matter of rule, merry-go-rounds and giant-wheels, and the famous so-called "Well of Death" (trick motorcycling inside consortium of wood-planks) are special attraction for children.
It is also a very important occasion from political point of view, as all the significant politicos, including the chief minister are there on the main day. Akalis and Congress hold separate stages to throw political dirt at one another. Such arrangement needs extremely tight police set-up which is met by calling out forces, sometimes even CRPF and BSF battalions from neighboring towns.