Consider Romans 16. The letters of Paul not only provide his theology, his “Gospel,” in the clearest possible terms. But his letters are thick with the details of his life, details that enable us to paint an extremely accurate portrait of his life and travels.
In Romans 16, Paul sends greetings to 26 named individuals, and two other individuals. Peter Lampe, a Lutheran New Testament scholar whose name I've mentioned, has done a complete analysis of Romans 16, in his 1987 (trans 2003) work “From Paul to Valentinus: Christians at Rome in the First Two Centuries,” MINNEAPOLIS: Fortress Press -- including a text critical and source critical study. Douglas Moo, in his commentary on Romans, relies on Lampe's work, as does Thomas Schreiner.
By sending greetings to all of these individuals (where the letter will be read in all of the churches in Rome), Paul seeks to remind those Christians in Rome who don’t know him, that he already knows a number of people from that city. These greetings "would encourage them to think favorably of him and remind the church as a whole of the number of 'supporters' that he already has" (Moo 918).
Moo also suggests that this list "makes clear is the pattern of church organization in Rome, for Paul identifies at least three, and perhaps five, separate house churches. Early Christians did not have large public facilities for meeting, so they used their own houses. And since even the largest house of the wealthiest Christian would hold no more than seventy or eighty for worship, growth beyond that point required that the Christians split up into house churches."
I've noted, too, that it was most likely that, in Rome, the Christians likely met near synagogues. Lampe has traced the locations of those synagogues (through archaeological and other means) and has even provided maps in his work.)
Lampe mentions the households of Aquila and Pricilla, and identifies four other “households” from the names in Romans 16. Then he continues:
Thus, in the capital city of Rome, we count five different Christian islands. If we assume that the other fourteen people of Romans 16 do not belong to any of these five crystallization points and that they hardly could all have belonged to only one other additional circle, then this results in at least seven separate islands of Christianity.Fast forward a couple of hundred years. What was the structure of the Christian community like in say the fifth century?
At least an eighth may be added to this when Paul sojourned in Rome and gathered Christians in his rented accommodation (Acts 28:30 ff). There is nowhere any indication of a central location for the different groups scattered over the city. Each circle of Christians may have conducted worship services by itself in a house or apartment, so that it can be referred to as a house community (see pgs 359-360).
We encounter the same phenomenon of local fragmentation [scattered congregations] if we proceed chronologically from the opposite direction and ask concerning the origins of the Roman titular churches (tituli).So here are words that modern day Roman Catholics will recognize: parishes, dioceses, baptistery, etc. Lampe actually lists these 23 titular churches, and then he continues his analysis to trace the “house churches” into the future, and the titular churches just listed, back into the past.
The Roman tituli of late antiquity are relatively independent parishes within the city (“quasi diocesis”), with their own place of assembly, their own clergy, cult, baptistery, and burial place. We know the number and the names of the tituli from the signature lists of the Roman synods. Some 25 titular parishes can be gleaned from the lists (pg 360, emphasis added).
The 15 to 20 pre-Constantinian titular house churches (most likely from the third century; cf. Cornelius in the middle of the third century [see Eusebius ”History” 6.43.11]) are indebted to private individuals who put space at the disposal of house communities…
The Christian fractionation stands against the background of a Jewish community in the city of Rome that was broken up into a number of independent synagogue communities [see detail provided here] [emphasis in original]. The parallelism is amazing, whether one wishes to consider the Jewish structure as a direct model for Christians or not.
Justin’s [community] met in a rented lodging “above the bath of Myrtinus”. In the same work, Justin attests that there are other house churches in Rome besides his. To the question, “Where do you assemble?” he answers, “There, where each one will and can.” “Or do you mean that we all are accustomed to assemble in the same place?" "It is by no means so.” Justin claims that he does not even know the other assembly places (Lampe pgs 364-65, citing Justin from “The Acts of Justin” see pg 276-277 in Lampe).
Lampe even goes into some detail about the structure of homes that Christians met in:
In view of the concurrence of archaeological and literary evidence, we may conclude that, in the first two centuries, there were no “house churches” in the sense of specific rooms permanently set aside for worship in secular houses. Positively speaking, the Christians of the first and second centuries celebrated their liturgy in rooms that were used in everyday life. This means that the rooms used for Sunday worship had no special immoveable cultic equipment. [This means, by the way, no altars, no tabernacles, no genuflecting, no “sacrifice of the mass.”] This explains the absence of any archaeological evidence of Christian assembly rooms in the city of Rome for the first two centuries. Christian circles met someplace in the basilica private of a wealthy Christian or on the third floor of an insula (cf. Acts 20:7ff.), in a rented lodging (over the bath of Myrtinus,” Justin, Acta 3), or in a suburban villa on the Via Latina (chap. 27). Justin witnesses that the gatherings of Christians in Rome took place where one preferred it or where it was possible. One was not limited to special cultic rooms.As he notes, the Christians have “no delubra et aras”; they are “a social gathering shunning the light, silent in public, loquacious in a corner.”
Still at the beginning of the third century, Minucius Felix lets the pagan Caecilius Natalis complain on the beach at Ostia at Christians: “Why do they take pains to hide the object of their worship….Why have they no altars, no known sanctuaries? Why do they never speak publicly, never meet openly? Lampe, 368-369).
I believe that every Christian who cares about the historical nature of his faith ought to be extremely grateful for the detailed picture of early Christian worship in the city of Rome, through a network of house churches, [secretive to evade persecution], without the leadership of single leader or publicly known bishop, naming only Christ as their Shepherd.