urban human settlements. The more organized sedentary life, in turn, led to a net increase in the birth rate. The large urban centres of Mohenjo-daro and Harappa very likely grew to containing between 30,000 and 60,000 individuals, and during the civilisation's florescence, the population of the subcontinent grew to between 4–6 million people. During this period the death rate increased as well, for close living conditions of humans and domesticated animals led to an increase in contagious diseases. According to one estimate, the population of the Indus civilisation at its peak may have been between one and five million. The civilisation extended from Pakistan's Balochistan in the west to India's western Uttar Pradesh in the east, from northeastern Afghanistan in the north to India's Gujarat state in the south. The largest number of sites are in Gujarat, Haryana, Punjab, Rajasthan, Uttar Pradesh, Jammu and Kashmir states in India, and Sindh, Punjab, and Balochistan provinces in Pakistan. Coastal settlements extended from Sutkagan Dor in Western Baluchistan to Lothal in Gujarat. An Indus Valley site has been found on the Oxus River at Shortugai in northern Afghanistan, in the Gomal River valley in northwestern Pakistan, at Manda, Jammu on the Beas River near Jammu, India, and at Alamgirpur on the Hindon River, only from Delhi. The southernmost site of the Indus Valley Civilisation is Daimabad in Maharashtra. Indus Valley sites have been found most often on rivers, but also on the ancient seacoast, for example, Balakot (Kot Bala), and on islands, for example, Dholavira. Discovery and history of excavation The first modern accounts of the ruins of the Indus civilisation are those of Charles Masson, a deserter from the East India Company's army. In 1829, Masson traveled through the princely state of Punjab, gathering useful intelligence for the Company in return for a promise of clemency. An aspect of this arrangement was the additional requirement to hand over to the Company any historical artifacts acquired during his travels. Masson, who had versed himself in the classics, especially in the military campaigns of Alexander the Great, chose for his wanderings some of the same towns that had featured in Alexander's campaigns, and whose archaeological sites had been noted by the campaign's chroniclers. Masson's major archaeological discovery in the Punjab was Harappa, a metropolis of the Indus civilisation in the valley of Indus's tributary, the Ravi river. Masson made copious notes and illustrations of