As far back as the prehistory, man has faced a problem of rain-water gathering and had adopted some solutions. One of the clever techniques to solve such a problem has been used by the inhabitants of the Sassi since the beginning vessels system.Little canals were obtained on the roofs of the houses. Water streamed into a reservoir put in the middle of a courtyard. In case of abundant rain the too full cistern started overflowing and water flowed down across a little canal into the reservoirs    of houses below and the next ones.There fore superfluous water was not dispersed but kept in the various reserves of the two quarters. In the “Sassi” some thousands of houses were caved and shared out in the so–called “vicinati”, courtyards or little half – circle shaped squares in common with ten families.Houses roofs acted as streets that can be travelled over on foot or by wheelbarrows (The drawing is drawn from the book "Giardini di Pietra" the author's kind consent).