1980s, the International Council on Monuments and Sites (ICOMOS) organised three conferences to assess possible nominations to the World Heritage List for sites in North Africa. It was unanimously agreed that Volubilis was a good candidate for the list and in 1997 ICOMOS recommended that it be inscribed as "an exceptionally well preserved example of a large Roman colonial town on the fringes of the Empire", which UNESCO accepted. City layout and infrastructure Prior to the Roman occupation, Volubilis covered an area of about , built on a V-shaped ridge between the Fertassa and Khoumane wadis on a roughly north–south axis. It was developed on a fairly regular pattern typical of Phoenician/Carthaginian settlements and was enclosed by a set of walls. Under the Romans, the city was expanded considerably on a northeast–southwest axis, increasing in size to about . Most of the city's public buildings were constructed in the older part of the city. The grand houses for which Volubilis is famous are in the newer part, behind the Decumanus Maximus (main street), which bisected the Roman-era part of the city. The decumanus was paved, with footways on either side, and was lined with arcaded porticoes on either sides, behind which were dozens of shops. The Arch of Caracalla marks the point at which the old and new cities merge. After the aqueduct fell into disrepair with the end of the Roman occupation, a new residential area was constructed to the west near the Wadi Khoumane. The city was supplied with water by an aqueduct that ran from a spring in the hills behind the city. The aqueduct may have been constructed around 60–80 AD and was subsequently reconstructed on several occasions. An elaborate network of channels fed houses and the public baths from the municipal supply and a series of drains carried sewage and waste away to the river to be flushed. The aqueduct ran under the Decumanus Secundus, a street that ran parallel with the Decumanus Maximus, and terminated at a large fountain in the city centre near the Arch of Caracalla. Most of the original pre-Roman city wall was built over or destroyed, but a stretch of the original wall, which was made of mud bricks on a stone foundation, can still be seen near the tumulus. The Roman city walls stretch for and average thick. Built of rubble masonry and ashlar, they are mostly still extant.