By about 1700 BC, the Harappan culture was on the verge of decline. The causes of its decline are not certain. The physical existence of the civilization ended due to various factors.
(a) Ecological changes led to the decline of land and agriculture, thereby enforcing the need to evacuate to other area might have been the reason for the disintegration of the Indus valley. Shifts in the monsoon pattern and changes in temperature led to the area more arid.
(b) Increase in population, excessive deforestation, decline in agriculture etc. might have created economic problems leading to the gradual decay of the culture. The marked decline in the quality of building and town planning indicates that the authorities were losing control.
(c) The changes in the river flow patterns and correspondent widespread flooding would have disrupted the agricultural base.
(d) The invasion of the Aryans is the other view that is said to be another reason which might have also led to the decline of the Indus valley. Thus ended the most brilliant civilization of the ancient world.