Built between 417 and 425 A.D. on top of some third century buildings, by then in ruins, at the behest of Empress Galla Placidia, the church is in the form of a Latin cross. It has a single nave with a wide transept, and an extended narthex (portico) joining the sacellum initially dedicated to Lawrence the martyr, into a single religious complex. The latter small building, also with a cruciform plan, is now known as the Mausoleo di Galla Placidia, definitively incorporated in the enclosure protecting the San Vitale complex.
Of the Church of Santa Croce, we can still admire the austere seventeenth century façade in reused bricks, the fifteenth century apse and the eighteenth century bell tower if, after the entrance to the Mausoleum, we continue along Via Galla Placidia. At present the church cannot be visited, but we know that the interior was once decorated with marble and wall mosaics.
On the outside, we can see the various renovations carried out between the seventh and eighth centuries when, between the late Middle Ages and the beginning of the seventeenth century, the church was gradually stripped of some of its parts and made into an independent building. Tradition has it that it was the church of choice of Empress Galla Placidia, who used to attend it late at night, prostrating and praying on the porphyry floor by candlelight.
The dedication to the Holy Cross by an empress of the Theodosian dynasty is not a random choice: the obvious reference is to the Basilica della Santa Croce a Gerusalemme, built in Rome by Helena, mother of Emperor Constantine I, and discoverer of the alleged True Cross. The iconography of the cross was in fact also of some importance to Galla who, as the daughter of Theodosius, had commissioned mosaics in the Basilica della Santa Croce in Rome and used the cross as a symbol on her coins.