These buildings, made in Italy, are part of the tradition of excavated houses that has been carried out for centuries throughout the Mediterranean basin and the Middle East. The sassi of Matera make up a network of excavated houses that connect with buildings on the surface in a spontaneous and capricious way. During the 1950s, due to their state of degradation, they were completely evicted, so that their 20,000 inhabitants had to be relocated to other neighborhoods. The abandoned houses became property of the State and walls were built to prevent them from being occupied. Later, in 1986, the Italian government invested 100 billion lire to recover this exceptional complex, which in 1993 was declared a World Heritage Site by UNESCO.