Library Eusebius of Caesarea Life of Constantine
Book 3, Chapter 35: Description of the Atrium and Porticos.
The next object of his attention was a space of ground of great extent, and open to the pure air of heaven. This he adorned with a pavement of finely polished stone, and enclosed it on three sides with porticos of great length.
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.