The Indus Valley, or Harrapan, civilization was discovered in 1920-21 when engraved seals were discovered near present-day Sahiwal in Pakistani Punjab at a place called Harappa. Excavations at Mohenjodaro in Sind discovered the buried remains of a civilization with a pictographic script. The Harappans first settled sites along the Indus River. This civilization extended to the Yamuna along the bed of the river Ghaggar in Rajhastan, Gujrat and up to the mouths of the rivers Narbada and Tapati. The Harappan culture extended from the Indus Valley through northeastern Afghanistan, on into Turkestan.
Most of the major sites of this civilization are in Pakistan. In fact it is in Pakistan that an earlier phase of it has also been unearthed. This happened between 1955-57 when a Pakistani archaeologist, F.A.Khan, discovered a town of the pre-Indus period 3300 to 2800 BC at Kot Diji in Khairpur, Sind. Such sites were also discovered by Rafique Mughal in Bahawalpur, in the Cholistan desert, extending the area of this culture to the whole of southern Pakistan.
The first appearance of this civilization was the early Harappan/Ravi Phase. This Ravi Phase, named after the nearby Ravi River, lasted from approximately 3300 BC, or even 3500 BC, to 2800 BC. This phase is related to the Hakra Phase, identified in the Ghaggar-Hakra river valley to the west, and predates the Kot Diji Phase (2800 -2600 BC), named after a site in northern Sindh near Mohenjo-daro. Increasing knowledge of the Ravi and Kot Diji Phase occupations at Harappa, and of contemporary settlements throughout northwestern South Asia, permits glimpses of later Indus Civilization.
Some of the most exciting discoveries in Ravi Phase levels have been of early writing. The origins of the Indus script-like signs dates from 3300-2800 BC. This would make the origins of writing in South Asia approximately the same time as in ancient Egypt and Mesopotamia.
The Indus Valley civilization is traditionally broken down into three more Harrapan Phase, from 2600 to 1900 BC, a Harrapan transitional period, 1900 to 1700 BC, and the late Harrapan period, 1700 to 1300 BC.
Archaeological and linguistic evidence indicates that the Dravidians were the founders of the Harappan culture. The Harappan civilization was twice the size the Old Kingdom of Egypt. They had trade relations with Mesopotamia, Iran, and the Central Asian peoples.
The Mature Harappan civilization is divided into two cultures, the Sorath Harappan and the Sindhi Harappan. The Sindhi Harappan sites are sites characterized by elaborate architecture, fired brick construction, sewage systems and stamp seals. The Sorath Harappan sites lack stamp seals, ornaments and elaborate architecture.
The Harappans were organized into chiefdoms, averaging between two and five acres. The Harappans were sedentary-pastoral people organized into various trades, such as, sailor-fishermen, smiths, merchants and farmers. The Harappans also possessed the social technology of writing seals.
The Harappans were find engineers and craftsmen. They cultivated wheat, barley and millet. The Harappans had a highly developed grain storage system. They built large cities with complex drain systems under the streets of some of their cities.
The Dravidians/Harrapans built the first major port in Lothol. Lothal was situated at the head of the Gulf of Cambay in Gujarat. Here archaeologists have found large warehouses ready to hold goods for export.
Due to changes in the environment of the Indus Valley, much of the area became more arid. This led to many Harappans migrating out of the Indus Valley into India, to settle sites in Gujarat, Punjab, Haryana and other parts of western Uttar Pradesh between 1700-1000 B.C. It was in Gujarat, that the Harappans probably first came in contact with the Aryans. The Harrapan civilization fell with the arrival of the Aryan race.