Ujjain has served as a center of science and culture in northern India. Since the fourth century B.C.E., it has served as the first meridian of longitude for Hindu geographers. It also numbers among the seven sacred cities of the Hindus, with the Kumbh Mela religious festival held there every twelve years. Ujjain is the home for Mahakaleshwar Jyotirlinga, one of the shrines to the god Shiva. Other noteworthy temples and palaces are also found in the city.