Indus Valley Civilization
The Indus Valley Civilization is one of the world's earliest urban civilizations. The civilization is believed to have existed during the period 3300 to 1700 BCE. It flourished during 2600 - 1900 BCE in the Indus and Ghaggar-Hakra river valleys primarily in what is now Pakistan and western India, extending westward into Balochistan. The mature phase of this civilization is known as the Harappan Civilization, after the first of its cities to be excavated, Harappa. Excavation of Indus Valley Civilization sites has been ongoing since the 1920s. The Indus Valley Civilization (or Harappan Civilization) was a Bronze Age civilization and spread over some 1,260,000 km², which makes it the largest ancient civilization.
The first excavation happened by chance in the year 1856. Around six miles from the river Ravi, railway construction workers came upon a small crumbling hill of fire-baked bricks in the foothills of the Himalayas. They quickly appropriated these bricks for the railway line's ballast. Along with the bricks, the also found certain steatite (soapstone) seals. Archaeologists, notably Sir John Cunningham, were quick to confirm their antiquity. This started a number of amazing excavations and discoveries in the region during which archaeologists unearthed the remains of an ancient civilization, which had its epicenter in the plains of the Indus. Since most of the excavations were close to the river Indus, it came to be known as the Indus Valley Civilization.
As the history of the Indus Valley Civilization goes, it is proposed that some 5000 years ago, nomadic people from Sumeria (modern day Iran) made their way into northwest India by means of the Mula Pass across the Himalayas, near modern Karachi. There they found a fabulously rich land, fertilized by five great rivers, namely Indus, Ravi, Beas, Chenab and Sutlej, which in the present forms the modern-day Punjab. Compared to the deserts of Iran, this area was God's blessed land, with ample supply of water, fodder and fuel. Clay was available in plenty in the riverbeds for making bricks, and so was wood to burn the bricks. Over a period of a thousand years, these immigrants spread over an area of half a million square miles, which gave rise to the Indus Valley Civilization
Around 1800 BCE, signs of a gradual decline of the Indus Valley Civilization began to emerge, and by around 1700 BCE, most of the cities were abandoned. In 1953, Sir Mortimer Wheeler proposed a theory that the decline of the Indus Valley Civilization was caused by the invasion of 'Aryans', an Indo-European tribe from Central Asia. He cited a group of 37 skeletons, as evidence, which were found in various parts of Mohenjo-Daro. He also cited the passages in the Vedas which referred to the battles and forts. However, the theory was soon rejected by scholars, since the skeletons belonged to a period after the city's abandonment and none were found near the citadel. Further examinations of the skeletons by Kenneth Kennedy in 1994 revealed that the marks, which were considered to be caused by aggression on the skulls were actually caused by erosion. Most of the contemporary scholars believe that the collapse of the Indus Valley Civilization was caused by drought and a decline in trade with Egypt and Mesopotamia. It has also contemplated that immigration by new peoples, deforestation, floods, or changes in the course of the river may have led to the collapse of the Indus Valley Civilization.