The circular city is emerging as new concept and form of practice in sustainable urban development. This is a response to the complex and pressing challenges of urbanization, as highlighted in the New Urban Agenda (NUA). The concept of a “circular city” or “circular city-region” derives from the circular economy model applied in the spatial territorial dimension. It can be associated with the concept of a “self-sustainable” regenerative city, as stated in paragraph n.71 of the NUA. This paper aims to develop an extensive form of “screening” of circular economy actions in emerging circular cities, focusing on eight European historic port cities self-defined as “circular”. The analysis is carried out as a review of circular economy actions in the selected cities, and specifically aims to identify the key areas of implementation in which the investments in the circular economy are more oriented, as well as to analyze the spatial implications of the reuse of buildings and sites, proposing a set of criteria and indicators for ex-ante and ex-post evaluations and monitoring of circular cities. Results show that the built environment (including cultural heritage), energy and mobility, waste management, water management, industrial production (including plastics, textiles, and industry 4.0 and circular design), agri-food, and citizens and communities can be adopted as strategic areas of implementation of the circular city model in historic cities, highlighting a lack of indicators in some sectors and identifying a possible framework for “closed” urban metabolism evaluation from a life-cycle perspective, focusing on evaluation criteria and indicators in the (historic) built environment.