The full circuit of walls had 34 towers, spaced at intervals of about one every , and six main gates that were flanked by towers. A part of the eastern wall has been reconstructed to a height of . The Tingis Gate, also reconstructed, marks the northern-eastern entrance to Volubilis. It was constructed in 168/169 AD – the date is known due to the discovery of a coin of that year that was deliberately embedded in the gate's stonework by its builders. An early medieval wall stands to the west of the Arch of Caracalla; it was built after the end of the Roman occupation, apparently some time in the 5th or 6th centuries, to protect the eastern side of the city's new residential area. It was oriented in a north–south direction and was constructed using stone looted from ruined buildings elsewhere in the abandoned areas of the city. Commerce During Roman times, Volubilis was a major producer of olive oil. The remains of buildings dedicated to olive pressing are still readily visible, as are the remains of the original presses and olive mills. One such building has been reconstructed with a full-size replica of a Roman olive press. Olive oil was central to the life of the city, as it was not just a foodstuff but was also used for lamps, bathing and medicines, while the pressed olives were fed to animals or dried out and used as fuel for the bathhouses. For this reason, even some of the grandest mansions had their own olive presses. Fifty-eight oil-pressing complexes have so far been discovered in Volubilis. They housed a standard set of elements: a mill, used to crush the olives, a decantation basin to catch the oil from pressed olives, and a press that comprised a counterweight, a prelum or cross-bar and the wooden supports within which the prelum was fixed. The olives were first crushed into a paste, then put into woven baskets that were subjected to pressing. The olive oil ran out into the decantation basin, to which water was periodically added to make the lighter oil float to the surface. This was then scooped out of the basin and poured into amphorae. There is also substantial evidence of the city being a lively commercial centre. No fewer than 121 shops have been identified so far, many of them bakeries, and judging from the number of bronzes