Brussels has grown from a 10th-century fortress town founded by Charlemagne's grandson into a metropolis of more than one million inhabitants. After the end of World War II, Brussels has been an important centre for international politics. It hosts the main institutions of the European Union, and the headquarters of the North Atlantic Treaty Organization (NATO). Brussels is the polyglot home of many international organisations, diplomats and civil servants. Brussels is the EU's third-richest city as of per capita income.