As you may know the Catholic Faith was illegal in the Roman Empire prior to 313 AD when the Emperor Constantine issued the Edict of Milan permitting the Christian Faith to publicly flourish. Prior to that time Church buildings as we know them today were rare. Mass was usually celebrated in houses.
Now careful here. These “houses” were usually rather large, with a central courtyard or large room that permitted something a little more formal than Mass “around the dining room table.” I remember being taught (incorrectly) that these early Masses were informal and emphasized an informal communal quality and were celebrated facing the people. Well that isn’t really true. People didn’t just sit around a table or sit in circle, not at all. They sat or stood formally and everyone faced one direction: East.
In the drawing above right you can see the layout of an ancient House Church from the excavated 3rd Century House Church at Dura Europos (Syria). Click on the picture for a clearer view. The assembly room is to the left and a priest or bishop is conducting a liturgy facing east at and altar against the east wall. A baptistery is on the right and a deacon is guarding the entrance door. The lonely looking deacon in the back of the assembly hall is there to “preserve good order” as you will read below. The Picture below left shows the baptistery of the Dura Europa House Church.
What is remarkable about these early liturgies is how formal they were even though conducted under less than ideal circumstances. The following text is from the Didiscalia, a document written in about 250 AD. Among other things it gives rather elaborate details about the celebration of the early Catholic Mass in these “House Liturgies.” I would like to print an excerpt here and make my own comments in RED. You will find that there are some rather humorous remarks in this ancient text towards the end.
Now, in your gatherings, in the holy Church, convene yourselves modestly in places of the brethren, as you will, in a manner pleasing and ordered with care. [So these "house liturgies were NOT informal Masses. Good order and careful attention to detail was essential]. Let the place of the priests be separated in a part of the house that faces east. [So, even in these early house Masses the sanctuary, the place where the clergy ministered was an area distinct from where the laity gathered. People were not all just gathered around a dining room table.] In the midst of them is placed the bishop’s chair, and with him let the priests be seated. Likewise, and in another section let the lay men be seated facing east. [Prayer was conducted facing to the east, not facing the people]. For thus it is proper: that the priests sit with the bishop in a part of the house to the east and after them the lay men and the lay women, [notice that men and women sat in separate sections. This was traditional in many churches until rather recently, say the last 150 years.] and when you stand to pray, the ecclessial leaders rise first, and after them the lay men, and again, then the women. Now, you ought to face to east to pray for, as you know, scripture has it, Give praise to God who ascends above the highest heavens to the east. [Again note, Mass was NOT celebrated facing the people as some suppose of the early Church. Everyone was to face to the east, clergy and people. Everyone faced one direction. The text cites Scripture as the reason for this. God is to the East, the origin of the light.]
Now, of the deacons, one always stands by the eucharistic oblations and the others stand outside the door watching those who enter [Remember, this was a time of persecution and the early Christians were careful only to allow baptized and bona fide members to enter the sacred mysteries. No one was permitted to enter Sacred liturgy until after having been baptized. This was called the disciplina arcanis or "discipline of the secret." Deacons guarded the door to maintain this discipline], and afterwards, when you offer let them together minister in the church. [Once the door was locked and the Mass begin it would seem that the deacons took their place in the sanctuary. However it also seems that one deacon remained outside the sanctuary and maintained "good order" among th laity.] And if there is one to be found who is not sitting in his place let the deacon who is within, rebuke him, and make him to rise and sit in his fitting place…also, in the church the young ones ought to sit separately, if there is a place, if not let them stand. Those of more advanced age should sit separately; the boys should sit separately or their fathers and mothers should take them and stand; and let the the young girls sit separately, if there is really not a place, let them stand behind the women; let the young who are married and have little children stand separately, the older women and widows should sit separately. [This may all seem a bit complicated but the bottom line is that seating was according to Gender and Age: the men on one side, the women on the other, older folks to the front and the younger ones to the back. Also those caring for young children should be in a separate area. See - Even in the old days there was a "cry room!"] And a deacon should see that each one who enters gets to his place, and that none of these sits in an inappropriate place. Likewise, the deacon ought to see that there are none who whisper or sleep or laugh or nod off. [Wait a minute! Do you mean to tell me that some of these early Christians did such things! Say it isn't so! Today ushers do this preserving of good order but the need remains!] For in the Church it is necessary to have discipline, sober vigilance, and attentive ear to the Word of the Lord. [Well that is said pretty plain and the advice is still needed].
One of the oldest House Churches was the House of Peter in Capernaum. There is evidence of a House Church where early masses were celebrated going back to as early as the 1st Century. Wall writings from that period were found. Over time the House Church was enlarged. After the Edict of Constantine a Byzantine Church was built on the site. But it was destroyed after the Byzantine period in the wake of Christian/Muslim conflicts. The whole area of Capernaum lay buried until the 1940s when it was rediscovered. Unfortunately in the 1960s a terribly ugly Church was built atop the ruins and it looks like a space ship that has landed on these ancient ruins. Here are a couple of videos that discuss the House and later House Church of St. Peter in Capernaum.