INDEX TO ALL NINE SECTIONS
Where Did The Early Church Meet?
From House Churches to Formal Buildings
Constantine, The Roman Pietas, and The Construction of Churches
The Basilica and The Great Hypostyle Hall at Karnak
The Edict of Thessalonica
Where Did The Early Church Meet?
We are so accustomed to 'doing church' in buildings that virtually have no other function that we forget that the ekklesia met exclusively in people's homes. In fact, the idea of churches that met in especially constructed buildings would have been completely foreign to the believers of the day
Day by day continuing with one mind in the temple, and breaking bread from house to house, they were taking their meals together with gladness and sincerity of heart, (Acts 2:46 NASB)
And every day, in the temple and from house to house, they kept right on teaching and preaching Jesus as the Christ. (Acts 5:42 NASB)
And when he realized this, he went to the house of Mary, the mother of John who was also called Mark, where many were gathered together and were praying. (Acts 12:12 NASB)
They went out of the prison and entered the house of Lydia, and when they saw the brethren, they encouraged them and departed. (Acts 16:40 NASB)
also greet the church that is in their house. Greet Epaenetus, my beloved, who is the first convert to Christ from Asia. (Romans 16:5 NASB)
The churches of Asia greet you. Aquila and Prisca greet you heartily in the Lord, with the church that is in their house. (1 Corinthians 16:19 NASB)
Greet the brethren who are in Laodicea and also Nympha and the church that is in her house. (Colossians 4:15 NASB)
and to Apphia our sister, and to Archippus our fellow soldier, and to the church in your house: (Philemon 1:2 NASB)
If anyone comes to you and does not bring this teaching, do not receive him into your house, and do not give him a greeting; (2 John 1:10 NASB)
As the Lord added to their numbers, the church grew, not by adding more and more people to a single group, or by constructing another building, but by multiplying sideways. A single group divided itself into other groups, much like an organic cell makes a copy of itself, and then splits into two new cells which, in turn, split again... making four new cells.
From House Churches to Formal Buildings
In support of this, there is a distinct lack of evidence for formal public church buildings, before Constantine made public Christian worship legal. The Khan Academy, a not-for-profit educational organization, has a very interesting article on their site, titled Early Christian Art & Architecture after Constantine. It describes how Christianity was radically transformed by the actions of a single man... Constantine, who was Roman Emperor from 306 to 337. Although the article is almost exclusively confined to Constantine's influence on the architecture of the period, the implications of his actions were very far reaching.
Prior to the time of the emperor Constantine, the earliest identified Christian church is in Dura-Europos, Syria. It dates from 235 AD. However....
".... there was not much that distinguished the Christian churches from typical domestic architecture. A striking example of this is presented by a Christian community house, from the Syrian town of Dura-Europos. Here a typical home has been adapted to the needs of the congregation. A wall was taken down to combine two rooms: this was undoubtedly the room for services. It is significant that the most elaborate aspect of the house is the room designed as a baptistry. This reflects the importance of the sacrament of Baptism to initiate new members into the mysteries of the faith. Otherwise this building would not stand out from the other houses. This domestic architecture obviously would not meet the needs of Constantine's architects. 
Some may point to the ancient Megiddo church, discovered in the grounds of the Megidddo prison in Israel, which dates back to the 3rd century AD. Although the structure does not follow the traditional building pattern for churches that emerged in the fourth century, this church is believed to be the oldest remains of a formal church in the Holy Land. However, anthropologist Joe Zias, former curator for the Israeli Antiquities Authority, disagrees.
"My gut feeling is that we are looking at a Roman building that may have been converted to a church at a later date."
His statement is partially based on an inscription in the church which mentions Gaianus, a Roman officer, who donated "his own money" to have a mosaic made. The inscription says Gaianus, "having sought honor, from his own money, has made the mosaic." As Joe Zias says
"If I were a Roman soldier in the third century, I certainly wouldn't want my name on (the church).… This would not have been a good career move. In fact, it sounds like the kiss of death.” 
How then did "church" began to be associated with large buildings in which Christians assembled on a regular basis?
Constantine and The Construction of Churches
Constantine and the Roman Pietas
We have to remember that Constantine was a Roman Emperor, who had a long history of constructing temples throughout the empire as a testament to Pietas, considered to be a primary virtue by the ancient Romans. Pietas, from which, I presume, we get our English word "piety", was variously translated as duty, religious behavior, loyalty, devotion, or filial piety. In fact, "the Romans sometimes attributed their misfortunes, individual or national, to lack of pietas". Therefore, many altars and temples, that had been wrecked during the civil war following Julius Caesar’s assassination, were rebuilt during the Pax Romana (a long period of relative peace and minimal expansion by military force), in 44 B.C. 
(As an aside, Michelangelo's sculpture of the body of Jesus on the lap of his mother Mary after the Crucifixion, is called The Pietà. It is housed in St. Peter's Basilica in Vatican City).
It was, therefore, very natural for Constantine to want to construct edifices in honor of Christianity. He not only built churches in the newly-constructed capital of Constantinople, but also did so in Rome, including the Church of St. Peter. Constantine was also responsible for building, among others, the Church of the Nativity in Bethlehem, and the Church of the Holy Sepulcher in Jerusalem. Additionally, Panagia Ekatontapyliani (also known as the Church of 100 Doors) is a historic Byzantine church complex in Parikia town, on the island of Paros in Greece. It dates to about 326 AD. and is believed to have been built by Helen, Constantine's mother.
The Basilica and....
Because the architectural style of the Roman temples were considered unsuitable, Constantine eventually decided on the architectural style of the Basilica, which had been used by the Romans for centuries.
The Roman basilicas had no known religious function; they were multi-purpose public buildings, used for commerce, a meeting place for the citizens, and as a court. They were usually large rectangular halls, consisting of a wide central aisle called the nave. Rows of pillars separated the nave from aisles on either side, which had high widows to let light in. The nave, or main aisle, usually ended in a semi-circular room called an apse, opposite the main door. As a law court, the magistrate would sit in the apse, usually on a slightly raised dais. The apse was also used as as audience halls of the emperors and governors.
The Photograph On The Right is of The Basilica of Constantine in Trier, Germany (also known as the Cathedral of Saint Peter) is the oldest cathedral in the country, dating back to to 340 AD. It is believed to have been built under Helen's direction, and is still used as a Catholic church today. Note the semi circular apse at the far end
The most famous of the Roman basilicas was the Basilica Ulpia, the largest, most lavish, and much admired basilica in Rome, named after Roman emperor Trajan, and probably completed in A.D. 112. The Catholic Encyclopedia says (All Emphasis Added)
In the basilica, when used as a place of Christian worship, dating from the fourth century, the whole congregation of the faithful could meet and participate in the ceremonies and devotions. The bishop took the place occupied of old by the prætor or quæster; the presbyters, the places of the assessors. Very little change was needed to erect a Christian altar on the spot in front of the apse, where the heathen had poured out their libations at the commencement and conclusion of all important business. The basilica of the heathen became the ecclesia, or place of assembly, of the early Christian community. 
One has to appreciate that the architecture of the Roman temples was rejected because of its pagan associations but, at the same time has to ask where the Basilica style of architecture came from.
The Great Hypostyle Hall at Karnak
The many rows of columns separating the side aisles, which are a traditional feature of basilicas, can be traced back to Egyptian Hypostyle Halls. Hypostyle was an ancient Greek term that described a building with rows of columns supporting its roof. In fact, the Basilica Ulpia is very similar to one of the most famous hypostyle halls... The Great Hypostyle Hall at Karnak.
The Egyptians believed that their temples were the actual dwelling places of the gods, Karnak being home to the god Amun-Re. As said by the web site of The Karnak Great Hypostyle Hall Project...
In antiquity, Karnak was the largest religious sanctuary in Egypt's imperial capital of Thebes (modern Luxor) and was home to the god Amun-Re, king of the Egyptian pantheon. For over 2000 years, successive pharaohs rebuilt and expanded the temples of Karnak, making it the largest complex of religious monuments from the ancient world. 
They describe the Hypostyle Hall at Karnak thus...
Covering an area large enough to accommodate the whole of Paris' Notre Dame Cathedral, the size and splendor of the Great Hypostyle Hall is enough to astound even the most jaded observer. The central nave is supported by twelve huge columns which are 21 meters (70 ft) high... These columns support a system of architraves and huge windows with massive stone grilles reaching a total height of around 20 meters (70 ft), similar to that of a Medieval cathedral. Flanking the nave are a further 122 columns, 12 meters (40 ft) high with closed-bud papyrus capitals. 
In short, the Christian basilica was built in the style of the temple of the Egyptian God Amun-Re.
And yes, I do understand that architecture is strictly a matter of windows, bricks, roofs and columns. But we are supposed to be a "called out" group of people... called to be separate from the world around us. We were never supposed to have church buildings at all. But we have wasted time, resources, and enormous fortunes doing exactly what every heathen culture in the world did... build religious monuments, one more grand then the next. Worse, we even patterned our so called "churches" after temples dedicated to an Egyptian God.
However this is far from the end of the story.
The Edict of Thessalonica
Some 40 years Constantine died in 337, Theodosius the Great became the last emperor to rule over both the eastern and the western halves of the Roman Empire. After the empire split, Gratian, his counterpart in the west, took steps toward legal persecution of heretics. This was followed shortly by the jointly issued Edict of Thessalonica, delivered on 27 February 380 by Theodosius I, Gratian, and his half brother Valentinian II.
Emperors Gratian, Valentinian And Theodosius Augusti. Edict To The People Of Constantinople.
It is our desire that all the various nations which are subject to our Clemency and Moderation, should continue to profess that religion which was delivered to the Romans by the divine Apostle Peter, as it has been preserved by faithful tradition, and which is now professed by the Pontiff Damasus and by Peter, Bishop of Alexandria, a man of apostolic holiness. According to the apostolic teaching and the doctrine of the Gospel, let us believe in the one deity of the Father, the Son and the Holy Spirit, in equal majesty and in a holy Trinity. We authorize the followers of this law to assume the title of Catholic Christians; but as for the others, since, in our judgment they are foolish madmen, we decree that they shall be branded with the ignominious name of heretics, and shall not presume to give to their conventicles the name of churches. They will suffer in the first place the chastisement of the divine condemnation and in the second the punishment of our authority which in accordance with the will of Heaven we shall decide to inflict. Given In Thessalonica On The Third Day From The Calends Of March, During The Fifth Consulate Of Gratian Augustus And First Of Theodosius Augustus. —Codex Theodosianus, xvi.1.2
The edict was significant for many reasons. Although the Doctrine of the trinity was a central focus of this edict (SEE), it was a joint effort by both Eastern and Western Roman Emperors to establish Christianity as the official state church of the Roman Empire. In addition to banning all pagan worship, and destroying pagan temples, Emperor Theodosius sought to make the Nicene version of Christianity the only permissible religion of the empire. Thereafter all their subjects were required to profess the faith of the bishops of Rome and Alexandria.
What is of special interest is that, in the Edict of Thessalonica, 'heretics' were forbidden to give "their conventicles the name of churches". Merriam-Webster defines the word conventicle as meaning an assembly for religious worship; especially a private meeting for worship not sanctioned by law. 
This edict, and others that followed, "established a pattern" of using the apparatus of the state to "suppress diversity of religious opinion". This would become "more pronounced as Theodosius' reign progressed".  Although the Edict of Thessalonica was largely aimed at the Arians, it did not take long for other "heretics" to run afoul of the emperors. As said by historian William Kenneth Boyd
Theodosius made the violation of divine law equivalent to sacrilege, and such violation involved the loss of certain rights of Roman citizenship. First, the power of leaving or receiving legacies, one of the distinctive privileges of Roman citizens, was taken from the Manichaeans in 381, then from the Eunomians in 389. Honorious extended this legal disability to the Donatists and Pricillianists, while Theodosius the Younger applied it to all sects. The right to hold office at court or in the army was withdrawn from the Eunomians by Theodosius; Honorious excluded all enemies of the Catholic sect from service in the palace; and, finally, Theodosius the Younger forbade heretics to take the military oath of allegiance or to serve in the imperial army. 
The Jews were similarly affected. Honorious and Theodosius the Younger excluded them from military and all other public services except municipal offices". A law gave "temporal officials the right to inspect and increase the taxes paid into the public treasury by the Jewish communities" 
The Gospel of Christ was well on it's way to becoming something Christ never intended it to be.
And, it did not stop there. As another example
In England there were three acts of parliament passed (in 1593, 1664, and 1670) to coerce people to attend Church of England services, and to prohibit unofficial meeting of lay people. Punishment initially included imprisonment without bail, and later a monetary fine for anyone, including a preacher, who allowed their house to be used as a meeting place. 
Why all this history? Simply because the events and edicts of the third and fourth centuries went a long way towards giving permanent form to Christianity as being a religion, the beliefs and practices of which were defined by self professed leaders, not the Bible.
In summary, Constantine made Christianity the state religion and built a number of churches fashioned after the Roman Basilicas, which were, in turn, modeled after The Karnak Great Hypostyle Hall. Karnak was the largest religious sanctuary in Egypt's imperial capital of Thebes, and was dedicated to the god Amun Ra. A few decades later another Roman emperor issued an edict forbidding "heretics" to call their "conventicles", churches. In other words, private meetings for religious worship was punishable by law.
CONTINUE ON TO CHAPTER III: The Four Main Reasons Modern Christians 'Do Church'. Worship and the "Worship Service". The Meaning of "Worship" As Defined by The Hebrew and Greek Words. Is "Worship" The Primary Reason Why Christians Are Supposed To Meet? Evangelism, The Sermon, Fellowship. The Primary Objective Of The Gathering Of Believers According to The Scriptures. Is The Church Supposed To Be a Largely Spectator Event? HERE
 Dr. Allen Farber. Early Christian Art & Architecture after Constantine.
 Greg Myre. Israeli Prisoners Dig Their Way to Early Christianity. The New York Times Company.
 Singapore Management University. Virgils Aeneas: The Roman Ideal of Pietas.
 The Catholic Encyclopedia. http://www.newadvent.org/cathen/01659a.htm
 The Karnak Great Hypostyle Hall Project. Welcome to the Hypostyle Hall. http://www.memphis.edu/hypostyle/welcome.htm
 The Karnak Great Hypostyle Hall Project. Dimensions. http://www.memphis.edu/hypostyle/about.htm
 http://www.merriam-webster.com/dictionary/conventicle. Emphases Added
 Dan Graves, MSL. Theodosius Issued an Edict Church History Timeline.
 William Kenneth Boyd. The Ecclesiastical Edicts Of The Theodosian code, Paperback edition (2008) from BiblioBazaar. Pg. 51
 ibid Pg. 53