Pagan Temples Re-branded as Christian Churches
One of the reasons Christianity managed to take over the Roman empire was its policy towards pagan temples. The latter were grand, ancient institutions dedicated to pagan gods. As Christianity moved from the purity of the apostolic age into Roman Catholicism, it too desired grandiose places of worship. As its political power grew after emperor Constantine (see picture below- this I took in Rome’s Capitoline Museum and it’s huge), it began to co-exist with and then rival the religious establishment. Eventually its power grew to such an extent that it was able to forbid the worship of the old gods. Rather than destroying these centres of paganism, they often renovated them.
The pictures (below and top) are of San Nicola in Carcere. You can see some columns from the temples of Juno and Janus built into the church’s sides. The Christian builders simply built around the temple, including its masonry into the new walls. This allowed the worshippers of the old Roman pantheon of gods to feel a little more comfortable in this new Christian jurisdiction.
The most famous example of all however, is the Pantheon itself (see below). Built by Agrippa at the time of emperor Augustus and later improved by Hadrian, this temple to all the Roman gods (‘Pantheon’) was consecrated to St. Mary and the Martyrs in 609: "Pope Boniface, asked the Emperor Phocas, to order that in the old temple called the Pantheon, after the pagan filth was removed, a church should be made, to the holy virgin Mary and all the martyrs, so that the commemoration of the saints would take place henceforth where not gods but demons were formerly worshipped." Exchanging the word god for saint and Jupiter for Christ was one way of telling the Roman populace that converting to the new-fangled religion would not be so painful as first imagined. It was just a rebranding exercise. This was successful in converting the people; I doubt that to which they converted was real saving faith in Christ; Catholicism often is a blending of Roman paganism with some New Testament theology.