South Asia's physical landscape has been shaped by its geography. The Himalayan and Hindu Kush mountains form barriers to the north, while the Arabian Sea, Bay of Bengal, and Indian Ocean surround it on three sides. The region is divided into three major regions - the northern mountains, northern plains, and Deccan plateau. The Himalayas and Hindu Kush mountains influence South Asia's climate and contain many of the region's major river systems like the Indus and Ganges.