Johannesburg is the largest and most populous city in South Africa. Johannesburg is the provincial capital of Gauteng, the wealthiest province in South Africa, and which has the largest economy of any metropolitan region in Sub-Saharan Africa. The city is one of the 40 largest metropolitan areas in the world , and Africa's only global city according to the Globalization and World Cities group's 1999 inventory, which classified it as a gamma world city). While often assumed to be South Africa's capital, Johannesburg does not form one of South Africa's three capital cities. Johannesburg does, however, house the South African Constitutional Court - South Africa's highest court.