The Macau Peninsula is the most populous and historic part of Macau. It has an area of 8.5 km² (4 x) and is geographically connected to Guangdong province at the northeast through an isthmus 200 m wide. The peninsula, together with downtown Zhuhai, sits on an island separated from the continent by distributaries of the Pearl River. The Border Gate (; Portuguese: Portas do Cerco) was built on the northern isthmus. At the south, the peninsula is connected to Taipa Island by three bridges, the Friendship Bridge (Ponte de Amizade); the Macau-Taipa Bridge (Ponte Governador Nobre de Carvalho); and the Sai Van Bridge (Ponte de Sai Van). The longest axis extends 4 km from the Border Gate to the southwestern edge, Barra (媽閣嘴). There is a western "Inner Harbor" (內港) paralleled by an "Outer Harbor" (外港) to the east. The 93 m Guia Hill (松山) is the highest point on the peninsula, which is has an average elevation of 50 to. Many coastal places are reclaimed from the sea. The Historic Center of Macau, which is entirely on the Macau Peninsula, became a World Heritage Site in 2005.