According to legend, the location of the First Church is obvious: the site of the Last Supper in Jerusalem, which was also the room where Pentecost occurred, and so on. That is the Centacle, and, as with every other even semi-Biblical site in the area, is the location of a lavish place of worship.
I am not so sure. As with most of these sites, their actual location is 'traditional', that is, established some centuries after the fact, so what was the second church?
Christianity differs quite sharply with paganism (and even Judaism) in at least one regard: pagan temples were meant as homes for Gods, not places for people to congregate. While some rites were, in fact, celebrated in public, these tended to be on the steps, or at the door of the temple. Inside, there might be a lamp or reed burning for the priests to find their way around, but aside from an image with a waist-high column in front, the room might be entirely featureless and dark.
Christian churches, on the other hand, were where people were. Many people at one time believed that the Early Christians met in the catacombs of major cities, but, as many people have seen when they actually tour them, there just isn't enough room for more than perhaps a dozen to meet at a time. Therefore, the earliest churches were most often located in family homes, in a very convenient place.
Most Roman houses, as you can see in diagrams, were in the form of two square suites, set one in back of the other. Originally, most families lived in a single round (or squarish) room, with a fireplace in the center and a walled yard in the back. As villages became cities, however, and overall prosperity increased, people began to curtain, and then to wall off little niches off this central room. Then, the walled garden in the back began to sprout a covered colonnade and from thence, more rooms. At the last, the rooms nearest the street would be walled off on the inside, and rented out for apartments and small businesses, leaving a large, often sooty-walled, space in the front with a hole in the roof, called the Black Room, or atrium, that most people had little use for, other than as a large corridor, with a decorative pool in the center. Some of the wealthier families used it as a kind of home office, somewhat extraneous for a small family, but ideal for gathering with a mixed group who might, as the need arose, read, sing and eat together, give one of their number a lustral bath, or engage in a little clandestine activity. ("Christians? I thought they were holding orgies!")
It is in this kind of church, in a city called Dura-Europos, in Syria that one might see the closest thing we have to a portrait of Jesus, painted about 232 AD.
It's on a panel about four feet high, and forms the upper part of a wall near the font. People who only know it from the Internet don't know it, and if you didn't know who or what to look for, the figures would look almost like a classical graffito or a child's drawing: a tall figure, carrying a bed frame, another figure lying on a similar bed, and, almost as an afterthought, a short, shaved man with short curly hair in a calf-length tunic pointing towards the bed. An imaginative viewer can see piercing eyes and high cheekbones. (It's also darker and redder than what you can see in published images.)
This. Is. Jesus.
The resemblance of this figure to Tolkein's drawings of hobbits is frightening. My mind is flashing to every crucifixion that I've ever seen, to the Children's Book of Bible Stories, to the thought: yes, He was of humble birth, though of a royal lineage, a man, like many other men, though born to greatness…and he looks like a hobbit?
Sorry if this upends someone's major mythology. Jesus was short, with curly short hair, and not at all 'regal' or 'royal' in his person. He looks like, well, given the circumstances, anyone of 'the people' in that period. But, isn't that the point?