After the Edict of Milan was issued, early Christians were allowed to meet freely for the first time. They needed a place to gather, and their churches were based on two types of pagan roman architecture, longitudinal and central plans. This was not the first time Christian art and architecture was based on previous pagan structures, for example, orant figures, people worshipping with their arms stretched out, can be pagan or Christian or Jewish.
The first type of church constructed was ordered by Constantine and built where St. Peter’s