Johannesburg is home to some of Africa's tallest structures, such as the Sentech Tower, Hillbrow Tower and the Carlton Centre. The Johannesburg city skyline has most of the tallest buildings on the continent and contains most international organisations such as IBM, Absa, BHP Billiton, Willis Group, First National Bank, Nedbank and Standard Bank. Many of the city's older buildings have been pulled down and more modern ones built in their place. North of the CBD is Hillbrow, the most densely populated residential area in southern Africa. Northwest of the CBD is Braamfontein, a secondary CBD housing many offices and business premises.