The suq or central market is located in a labyrinth of streets and alleyways in the centre of the old city of Sana'a. A large variety of merchandise is offered for sale yet sectors specialising in specific commodities make shopping comparatively easy. Surrounded by a massive 20 to 30-foot high wall, old Sana'a is one of the world's oldest inhabited cities. Several stone and brick buildings date back to the 11th Century AD; many are over 400 years old. Modern buildings follow the same 1,000-year-old distinctive Yemeni architectural style. In 1986, the city was designated a World Heritage Site by UNESCO after work had begun to restore many fine but neglected buildings.