Library Eusebius of Caesarea Life of Constantine
Book 4, Chapter 59: Farther Description of the same Church.
Such was the magnificence with which the emperor was pleased to beautify this church. The building was surrounded by an open area of great extent, the four sides of which were terminated by porticos which enclosed the area and the church itself. Adjoining these porticos were ranges of stately chambers, with baths and promenades, and besides many apartments adapted to the use of those who had charge of the place.
English translation by Ernest Cushing Richardson, in Nicene and Post-Nicene Fathers, Series II, Vol. I (eds. Philip Schaff and Henry Wace; Buffalo: Christian Literature Publishing Co., 1890). Public domain. Digital text via New Advent Church Fathers.