From the first Domus Ecclesiae to the sacred buildings of the first Christian church, which over time acquire a monumental physiognomy radically distinct from the traditional religious architecture of antiquity. A fundamental introduction to the architecture of the first churches of Rome. The volume by Hugo Brandenburg has become the international reference work on the first churches of Rome, an extraordinary building phenomenon which, following the Milan edict of 313 issued by Constantine and the co-regent Licinius, made Rome the first center of expression and diffusion of the new art that we call "paleo-Christian". The reading of the Scriptures, the psalmody, the homily and the divine banquet that characterized the meetings and worship practices of the first communities - and even after the apostolic age - took place in large private rooms, or other buildings made available by a member of the community, not yet constituting a recognized religious association with its own legal status, and not being able to own real estate. Unlike temples or pagan buildings of worship, sanctified by the presence of the god, whose worship took place mostly outside, the divine service of Christians always took place indoors. From the end of the second century, with the growth of communities, it became necessary to have specific spaces destined for worship, places that will be defined domus dei or domus ecclesiae, from the Greek term that originally designated the community itself, the assembly of believers, to whom will gradually be attributed the sacredness that will make it the "temple of God". But we will have to wait until the Constantinian era for these places to begin to present a particular architectural physiognomy and acquire, in the Christian Church, the monumental physiognomy that we can still admire.