Now that we have the context for how Roman/Greek temples and homes became the structural foundation for Roman churches, let approach some churches. Before we enter, we see the facade and step between the columns that define the portico. The image to the left is what we usually think of for a Roman church. In this case, we are looking at the facade of Basilica of St. Maria Maggorie. You can see the central entrance line with columns, the inward curve on the second level (the loggia), topped with statues and campanile (bell tower). However this facade was not added to the basilica until the 18th century.
The church structure has gone through centuries of changes. The original structure was built, per legend, during the 4th century, after a miracle occurred on this site. The 5th, 13th, 14th, and 17th centuries saw additions, both to the exterior and interior. The columns and arches of the loggia were added in the 17th century, obscuring the 12th century mosaics. Fortunately, you can join a tour which take you up the loggia for grand views of the piazza in front of the church and those hidden mosaics.
To get back to the 12th century and view what this facade might have looked like, cross over the Tiber river to the Basilica of St Maria in Trastevere. This church, in a quiet neighborhood, retains it piazza and mosaic loggia facade.
While you cannot get as close to the mosaics as you can on the tour of the loggia at St. Maggorie, you are drawn into the church with images of that the church represents. For some, this may be an experience of grandeur; For others contemplation; For other connection. In any case, unless you intent is to check off another item on a bucket-list, entering a church is intended to have an experience. The facade announces that this is the place, different from a home, shop, or entertainment facility.
The portico serves a similar purpose. upon passing through the columns, the distractions of the street and outside world begin to fade. For many churches in Rome, the portico is more than a transitional zone of shade and cool air from the stones that now surround you. Many churches display their history through statues, artifacts, and plaques embedded into the walls.
The wall inside the portico of St. Maria in Trastevere is covered in ancient stone plaques. Were I able to read Latin, I might be able to decipher some of them. But, in some cases, pictorial images speak for my lack of language skills. Notice the dove with a branch in the lower right corner of the plaque.