Blindfolded camels are still used in the suq to grind sesame and mustard seeds in huge pestles and mortars. As this camel walks round and round all day, it grinds mustard seed to extract the oil. Surrounded by a massive 20 to 30-foot high wall, old Sana'a is one of the world's oldest inhabited cities. The suq or central market is located in a labyrinth of streets and alleyways in the centre of the old city. A large variety of merchandise is offered for sale yet sectors specialising in specific commodities make shopping comparatively easy.