Cities consume over 75% of natural resources, produce over 50% of global waste and emit 60 - 80% of greenhouse gases. The scenario that by 2050 two thirds of the world population will live in cities, highlights how cities are still responsible of the growing consumption characterized by linear economy processes, with the production of various types of waste. In this unsustainable framework, the Circular Economy offers the opportunity to shape the urban system by means of rethinking the possibility to produce and use goods and services exploring new ways to ensure long-term prosperity. The Circular City paradigm contains in fact all the principles of the Circular Economy: recovery, recycling and sharing. In particular, Circular City also introduces actions related to the development of renewable energy communities, use of green materials, CO2 absorption approaches and Proximity Cities. The aim of this work is to develop a methodology to build a composite index (Circular City Index) capable of measuring the degree of implementation of urban policies that enable the territory to initiate an ecological transition of public assets. The city of Cagliari (Sardinia, Italy) represents the case study to apply circular urban policies in public properties, for civil and military use.