The region is known for the Indus Valley Civilization, which was responsible for the birth of ancient culture of the Indian subcontinent. The flat and fertile terrain has facilitated the repeated rise and expansion of various empires, including the Maurya Empire, Kushan Empire, Gupta Empire, Pala Empire, Imperial Kannauj, Delhi Sultanates, the Mughal Empire and Maratha Empire – all of which had their demographic and political centers in the Indo-Gangetic plain. During the Vedic and Epic eras of Indian history, this region was referred to as "Aryavarta" (Land of the Aryans). According to "Manusmṛti" (2.22), 'Aryavarta' is "the tract between the Himalaya and the Vindhya ranges, from the Eastern Sea (Bay of Bengal) to the Western Sea (Arabian Sea)". The region is also referred to as "Hindustan" or the Land of the Hindus, as mentioned in the Sanskrit shloka in Vishnu Purana: