Three in every five people alive are here. Asia holds about 4.8 billion people across 44 million square kilometres, which makes it both the largest continent and the one where almost every superlative on the planet ends up: the highest mountain and the lowest dry land, the deepest lake and the largest, the wettest inhabited place and one of the driest deserts, the biggest country by area and the two biggest by population. The course starts where the continent starts — with a collision. India is still driving north into Asia at a few centimetres a year, and that slow crash built the Himalaya, lifted the Tibetan Plateau to an average of 4,500 metres, and set up the monsoon that feeds half the world. Everything downstream follows from it: the Ganges, the Indus, the Mekong, the Yangtze and the Yellow River all start in the same high ground, and the farming those rivers allow is why the two largest populations on Earth are where they are. Then the regions, four episodes across them. East Asia, from a China of 1.4 billion and 34 province-level divisions to a Japan that is 73 percent mountain and sits on four tectonic plates. South Asia, where India alone has 22 scheduled languages and more people than Europe, Africa or the Americas. Southeast Asia, mainland and archipelago, where Indonesia strings 17,000 islands across three time zones. And Central and West Asia, the steppe and the Silk Road, the Gulf and its oil, and the ground where Judaism, Christianity and Islam all began — as Hinduism, Buddhism, Sikhism, Jainism, Shinto, Taoism and Confucianism began elsewhere on the same continent. It ends where most Asians now live: in cities, thirteen of the world's twenty largest among them.