Baku (, ; , ) is the capital and largest city of Azerbaijan, as well as the largest city on the Caspian Sea and of the Caucasus region. Baku is located below sea level, which makes it the lowest lying national capital in the world and also the largest city in the world located below sea level. Baku lies on the southern shore of the Absheron Peninsula, alongside the Bay of Baku. At the beginning of 2009, Baku's urban population was estimated at just over two million people. Officially, about 25% of all inhabitants of the country live in Baku's metropolitan area. Baku is the sole metropolis in Azerbaijan.