Description of the Double Porticos on Either Side, and of the Three Eastern Gates
Besides this were two porticos on each side, with upper and lower ranges of pillars, corresponding in length with the church itself; and these also had their roofs ornamented with gold. Of these porticos, those which were exterior to the church were supported by columns of great size, while those within these rested on piles of stone beautifully adorned on the surface. Three gates, placed exactly east, were intended to receive the multitudes who entered the church.
Source: Life of Constantine (New Advent)