||THOLOS-CISTERNS, BELL-CISTERNS AND PIT-CISTERNS
Definition characters description and diffusion
The digging of underground ogive cisterns is a practice diffused in the whole world up until the Neolithic period. The tanks serve to contain water of sporadic origins therefore they must have enlarged forms to increase capacity. In karst soils, the cisterns are excavated in the limestone rock with very precise ogives. The most archaic tanks are not waterproofed. If the limestone is not cracked a natural waterproofing is formed with the depositing of a coating on the walls. The perfect curves and surfaces accurately worked further the phenomenon. The bell-shape that widens in the subsoil is due to the necessity of having inputs very close sufficient enough to pierce the hardest rock on the surface and allow the digger to expand the cavity inside where the limestone is more tender. The tanks are supplied with waters from rain and those flowing down slopes where collection surfaces are organized, cabalettas and decantation devices for the water. From the perfectly parabolic forms of the bell tanks prevalent in the Neolithic of the Balkans, Southern Italy and Malta, there is a switch to more elongated ‘tholos’ forms in the age of metals present in Crete and Mycenae, and to cisterns with a more vertical tank well spread by the Phoenicians and various types of cisterne a camera. These are a great development in all antique civilizations with the spread of the techniques of coating and stone vaults and waterproofing. For this purpose lime based plasters, pozzolan, organic compounds or earthenware are used.
General characters description and diffusion
Large bell-shaped cisterns are dug inside the caves to harvest water dropping from the slope, which is conveyed by a network of little channels. In some circumstances, a cistern built at the bottom of the cave fills up with water even though it is not connected to channels. In that case the cave soaks up the exterior moisture which condenses on the colder bottom wall and drops down into the cisterns. In the pre-Columbian civilisations the practices of landscape modification to build rainwater harvesting systems on a large scale by creating water intakes along the slopes, dams and watersheds, predate the monumental architecture and date back to the 1st millennium BC (Scarborough and Isaac, 1993). In the inland areas of Yucatan the Mayas had to solve the problem of finding sufficient water resources in all seasons in order to meet the needs of the massive urban areas and of agriculture. These needs could not be satisfied by the natural cave reservoirs or by the cenote pools alone. Moreover the latter were subject to the seasonal changes in level, to salinity due to the link with the underground passages down to the sea or to desiccation by obstruction of the tunnels. Bell-shaped cisterns called chultun were dug out of the stone to obtain drinking water supplies. The entrance is as narrow as possible to reduce the area of drilling of the strongest surface layer. It allows the passage of the digger which enlarges the excavation in the subsoil and forms a pseudo dome. The parabola-shape perfectly smooth had spread since the Neolithic Age when the cisterns were not whitewashed. As a matter of fact, if limestone was intact it made the cisterns impermeable by forming a superficial coating. In ancient and medieval age the walls of cisterns were insulated by means of plaster made out of lime and shards, called coccio-pesto. They generally featured a basin for water decantation and sedimentation at the bottom. Cisterns on the highland of Murgia and in Matera had an average depth of 3 up to 4 metres and a width of the same size at the bottom. Each cistern had a capacity of about 9 m3 of rainwater which depended on the catchment area made out of the slope, the streets network and the pitched roofs. Their urban use is now outdated for the introduction of modern networks. They are still used in rural areas and are being reintroduced in the restored Sassi of Matera to produce water for health purpose by means of a dual network. Cisterns give a substantial contribution to the decrease of drinking water consumption.
Advantages and sustainability
Cisterns are used to collect and store water. This water is very important because it makes other vital human processes necessary.