A day after the Hindu festival of Holi, Sikhs around the world celebrate Hola Mohalla – an exhibition of the Sikh martial spirit. The center of this celebration is at Anandpur Sahib in Punjab, India:
This custom originated in the time of Guru Gobind Singh (1666-1708) who held the first march at Anandpur on Chet vadi 1, 1757 Bk (22nd February, 1701). Unlike Holi, when people playfully sprinkle colored powders, dry or mixed in water, on each other the Guru made Hola Mahalla an occasion for the Sikhs to demonstrate their martial skills in simulated battles. This was probably done forestalling a grimmer struggle against the imperial power following the battle of Ninnohgarh in 1700. Holla Mahalla became an annual event held in an open ground near Holgarh, a Fort across the rivulet Charan Ganga, northwest of Anandpur sahib.
Read more about Hola Mohalla at sikhiwiki.org.