A place of confluence, of contrasts and conflicts that cyclically emerge, the Mediterranean, a space between lands, unites the peoples that surround it in the affinity of its roots and in the unity of its history. A polar and composite identity, therefore, based on fusions, separations, entanglements, exchanges, raids, battles, which often tends, despite everything, to recompose itself, recognizing something maternal in the mass of water, which leads to a common responsibility . The reason for this book, which develops the themes of a conference held in Naples with extraordinary commitment to research, lies precisely in the sharing of this sense of responsibility by the scholars who responded with passion to our appeal. The center of gravity of the great epochal transformations has long since shifted, compared to the sea which saw the birth of the three great monotheistic religious traditions around it; but it is also true that some of the crucial problems of our time have their geographical location here and the comparison between West and East has one of its most delicate "sensors" here. In fact, until a few decades ago, two different perspectives existed on the two opposite sides of the Mediterranean with respect to common history. The story of the Crusades, interpreted ideologically, was the litmus test of mutual misunderstanding and mistrust, which is hard to eliminate. Today, much has changed and there are many symptoms of further future changes that will encourage dialogue and collaborative research. This is demonstrated by the material collected for this book by scholars from both sides with similar methodologies, all based on philological rigor and the tools of common knowledge. A season of "Mediterranean studies" is on the horizon, fueled, without distinction of quality, by Islamic and Western culture; and it is no coincidence that one of the most fertile meeting grounds has proven to be that of the city's history. At a time when, all over the world, the city is going through an identity crisis, the area in which the city itself originated and developed harmoniously, experimenting with forms of aggregation, hierarchies, partitions, dimensions and spatial models the most diverse - but always comparable with the needs and desires of citizens - can still teach us many things to use in the future. Perhaps the choral breath of the Mediterranean city is its highest value, which is usually missing in the modern city, the secret to investigate, the value to reflect on to acknowledge that common "sense of responsibility" that it is right to talk about. The essays collected here help to focus on this choral breath, to find it in different situations and eras, like a chrism of Mediterraneanness.