Pakistan traces its history back to at least 2,500 years before Christ, when a highly developed civilization flourished in the Indus valley areas. Excavations at Harappa, Moenjodaro, and Kot Digi have brought to light evidence of an advance civilization existing about that time. Round about 1,500 B.C., the Aryans overwhelmed this region, and by and large, influenced the Hindu civilization whose centre moved to Ganges valley, further east. Later, the Persians occupied northern regions in the 5th century B.C. The Greeks came in 327 B.C., under Alexander the Great, and passed away like meteor. In 712 A.D., the Arabs, led by Mohammad Bin Qasim landed near Karachi, and ruled the lower half of Pakistan for two hundred years. During this period Islam took roots in the soil and influenced the life, culture and traditions of the people. In the 10th century A.D. began the systematic conquest of South Asia by the peoples from Central Asia (Tajikistan, Kyrgyzstan, Uzbekistan, Turkmanistan, Khazakhistan, Mongolia etc.), who ruled almost the whole subcontinent upto 10th century A.D., when the British occupied the land and ruled for nearly two hundred years, but for only 100 years over what is Pakistan now.