Pakistan is located in South Asia, at the crossroads of the Middle East and Central Asia. It has a coastline along the Arabian Sea in the south and is bordered by India, Afghanistan, Iran, and China. Islamabad is the capital, while Karachi is the largest city and main port. Pakistan's geography is dominated by the Indus River, which flows the length of the country and sustains its agricultural heartland. The north and west are home to some of the world's highest mountains, including K2, the second-highest peak on Earth, located in the Karakoram range. The western part of the country features the arid Balochistan Plateau, while the east contains the Thar Desert. Pakistan has a diverse climate, from temperate in the north to tropical in the south. It is the world's fifth-most populous country and has a rich cultural heritage influenced by various civilizations that passed through the Indus Valley.