Now one of the 10 biggest cities in the world, the area surrounding Karachi has been inhabited for millennia. It only became a fortified settlement, and the seeds of a city proper, in 1729. The growth was spurred by becoming a major seaport connected to an extensive railway network. At the time of the Partition of India in 1947, the population was still 'only' around 400,000. It became the primary destination of Muslim immigrants from India in the 50s and 60s. Pakistan has not had a census since 1998 (at which time less than 10 million lived in Karachi), but the population is estimated to be anywhere between 15 and 24 million people. An estimated 45,000 new migrants settle in the city every month. It is a melting pot of people from all over Pakistan, Bangladesh, Myanmar and Sri Lanka.