Water System
Sillyon water system has two different development areas, namely the Acropolis and the Lower City. There are numerous cracks, fractures and voids in the limestone unit of Sillyon, which is established on a hilly area on Gebiz limestone formation. For this reason, it holds precipitation and surface waters and contains groundwater. In the surveys carried out on the slopes of the city, water outlets were attested at the contact zone of claystone and limestone at approximately 130-110 m altitude. In other words, the groundwater level follows the contact of Gebiz limestone and the Karpuzçay formation and a few meters above it and springs out from this level as a source. In parallel with the urbanization of Sillyon, these water outlet points were integrated into the city plan and used in many buildings. In the western part of the city, a Roman Baths in the Roman Imperial period, Nymphaion A in the Late Antiquity and a fountain in the Ottoman period were built on the water outlets in the Lower City.
The columned cistern at the Acropolis
In fact, after the water source was accumulated in a water tank in the Byzantine period, it was transferred to the plain via an Aqueduct for irrigation purposes. The water source in this area is still used today. The Structure with Dromos located on the southern slope of the city was also built on a water source. Today, the water outlets used by locals to water their animals are located in the north. As can be seen, the geology of the city determined the water supply system and urban planning developed accordingly in most places.
The water system at the Acropolis is based solely on cisterns and wells. In the ancient city of Sillyon, built on top of steep rocks, numerous cisterns were hewn to store rain water and reduce the effect of precipitation. About 220 cisterns were attested in the city. In general, the cisterns are pear-shaped well type. Their mouths were fitted with a curb and closed off with a stone lid. That many of them have survived in a very good condition is worth noting. In the surveys carried out at the Acropolis, the 220 cisterns attested were categorised under four types. Although their widths vary, their depths are in the intervals of 3, 4.5, 6 and 8 m respectively. The 8-m-deep cisterns call for attention among all types and are called public cisterns; these cluster in areas with public structures. Furthermore, there is a rectangular cistern with 15 columns, just south of the Kastron, and it is the most prominent structure of the Acropolis water supply system.