“Pellegrini e Pagani a Roma” is the new historical essay book by Vincenzo Cohen on the forms of religious expression that have marked the sacred architecture of ancient Rome. The text, organized according to a breakdown by areas of the capital, is a guide to the reading of monuments as an artistic expression of pagan and Christian rituality and the subsequent forms of religious syncretism. The spread of the Christian cult operated by the apostles in the Roman ideological-cultural panorama, opens the way to a new great phase of history, not exempt from bloody repression and doctrinal disputes, which will initiate the gradual process of the affirmation of Christianity in the Occident. In the course of history the personalities of the emperors will embrace their respective faiths from time to time by conveying languages and artistic manifestations towards forms of political propaganda. Secret places of worship will be born during the anti-Christian persecutions constituting the origin of the new Christian groups, while pyres of burning corps will illuminate the nights of the eternal city. The advent of Christianity, if on the one hand it will overshadow the previous religious expressions, on the other it will help to perpetuate the historical memory of the places, preserving their testimonies. With the process of Christianization started in the IV century A.D. by the Emperor Constantine, the gradual irradiation of Christianity will begin through the erection of large basilicas born on the places of martyrdom and along the routes of the Christian pilgrimage, which will lead to the definite effermation of the Papacy. In the age of the Barbarian kingdoms, new leaderships will adhere to the Arian heresy by seeing in the religious practice a means through which to implement the cultural unification of peoples. After the coronation of Charlemagne, the process of cultural renewal initiated by the Western Church found its peak with the institutionalization of relations between the Papacy and the Empire. At the same time, the presence within the Roman artistic world of secular institutions and pagan pre-existences, will testify the presence of parallel forms of religiosity linked to the phenomenological world of natural magic from which will born mixtures of sacred and profane, that from classicism to today, have contributed to feed the dark side of the city of Rome.