The configuration of India is primarily divided into three distinct regions with sharply differentiated features - the Himalayan region, the Indo-Gangetic plain and Deccan plateau.
The crescent shaped Himalayan range running from Afghanistan in the north to Assam in the east has a length of nearly 2,560 kms. with an average breadth of 240 to 320kms. The Himalayas contain altogether about 114 peaks of over 20,000 feet, of which 75 exceed 24,000 feet. The best known are Everest or Gourishankar (29,140 feet), the highest mountain peak in the world, Kanchanjangha (28,176 feet), Dhaulagiri (26,826 feet), Naga Parvat (26,620 feet) and Nandadevi (25,661 feet). The three lifelines of India, river Indus in the west, the holiest of holy, river Ganga in the centre and Brahmaputra in the east flow from the Himalayas. The perennial snows of the Himalayas are as important to the hydrography of India as the two monsoon winds.
The river Indus (about 2880 Kms. of the total length) rises from the Kailas Mountain and flows through Punjab and Sindh, which prevents the region from turning into a desert. It receives water from five tributaries, Sutlej (Verdic Satadru), Chenab (Vedic Asikini or Chjandrabhaga), Ravi (Vedic Parusni or Iravati), Beas (Vedic Vipasa) and Jhelum (Vedic Vitasta). The Indus is navigable for about 1280 Kms. that is upto Dera Ismail Khan. The Ganga (2480 Kms long) rises in the central Himalayas in a glacial ice-cave known as Go- mukh (cow's mouth) and reaches Haradwar after flowing 288 kms.
Thereafter it is joined by its Himalayan tributaries, the Jamuna (which joins it at Allahabad), the Gogra, the Gandhaka and the Kosi and other tributaries like Chambal and Son. After reaching the ancient Gauda kingdom the Ganga divides itself into two branches namely the Bhagirathi (Hoogly) and Padma. Brahmaputra (about 2880 kms. long) originates at the eastern base of Kailas Mountain and flows through Tibet under the name Tsan-Po. It enters India near Sadiya in Assam under the name Dihang. Then Dibang and Luhit join it and the united stream is known as Brahmaputra. Passing through Assam it joins Padma. It is navigable upto Dibrugarh in Assam for a distance of about 1200 Kms.
The Himalays are famous as the abode of gods, goddesses and sages. It houses the famous lake Moanosarovar, one of the holiest of places for the Hindus. Goddess Parvati was the daughter of the Himalayas. Kailash, the abode of Lord Shiva is a part of the Himalayas. Kalidas has described it as the King of mountains or nagadhiraji and ensouling divinity or devatatma. It contains many important and popular hill-stations like Darjeeling, Simla, Kulu, Manali etc.
Its outer ranges, which touch the northern plains, are called the 'Sivaliks'. The west of the Himalayas is the Hindukush mountains parts of which are now included in Afgahanistan. Further south there are Safed Koh, Sulaiman and Khirthar mountains as the north-western boundary of India. In the east there are Patkoi Hills, Naga Hills, Khasi Hills, Garo Hills, Jaintia Hills, Lushai Hills, and Chin Hills. The Himalayas also contain some high plateaus and valleys like the Kashmir valley. The green valley at an elevation of 6000 feet is about 132 Kms. long and 40 Kms. broad, it has been justly regarded as "the earthly paradise". The protective cover of the Himalayas has given to India its civilization and social structure from the earliest times to the present day. The thick Tarai forest borders the central Himalayas.
The mountains form an impenetrable defensive rampart of India against any invasion. These are so steep and so densely forest-covered that the crossing becomes almost impossible. However, the Khyber, Gomal, Kuram. Tochi and Bolan passes in the Himalayas have often served as the highways of active interaction with the outside world by way of foreign invasion and racial immigration. The Aryans, the Persians, the Greeks, the Scythians, the Parthians and the Kushanas during ancient period and the Mongols during medieval and the Chinese during recent times have entered through these routes. Almost all the foreign invaders to India except the Europeans have entered through these passes.
In the north-west, the Khyber pass (about 32 Kms. long) with the city of Peshawar (ancient Purushapur) at its mouth opened the road to Kabul. Kabul as such was well connected by land route to a number of places of Central Asia and Asia Minor. Similarly, through Bolan Pass the road reached Kandhar, another great meeting-place of ancient routes to Persia Lying between Afghanistan and Dera Ismail Khan, the Gomal route was shorter and safer Another line of communication, which passed through the inhospitable Makran region along the coast of Beluchistan, connected Persia (Iran). This was the route followed by Alexander on his return journey. Through these routes from time immemorial, migrating tribes, peaceful traders and conquering armies have entered India.
By protecting India from the dry cold winds blowing in from Tibet and serving as a great screen for the monsoon winds it has increased the fertility and prosperity of the Gangetic plain. The numerous rivers fed by the glaciers of the Himalayas act as an inexhaustible and perennial source of water. The rivers, too, are powerful determinants in the life of country.