The earliest Indian civilization was that of the Harappans. The Harrapans boasted a number of large cities. The Harappan civilization gave way under the weight of the Aryan invasion. The Aryans arrived around 1500 B.C. and brought about an abrupt end to the Harrapans. The Aryan period lasted for over 1,000 years. During this time, many of the social and religious norms that have become associated with India came into being. The caste system arose during this period, as did Hinduism and Buddhism. In 326 B.C., Alexander the Great briefly invaded India. From 326 B.C. until 183 B.C., the Mauryan dynasty ruled India. With its collapse, India fell into disunity.
At about 100 B.C., the Kushan Kingdom developed in Northern India and the area that would become Afghanistan. In 300 A.D., the Kushan Kingdom came to an end and was replaced by the Gupta Dynasty, which ruled Northern India. The Guptas established a classical age in Indian civilization. With the fall of the Guptas at the end of the 5th century, Indian again descended into disunity. At the end of the 10th century, the Empire of Mahmud and Ghazni, founded by a former Turkish slave, extended its rule into Northern India. For the next four centuries, India consisted largely of independent feudal districts.