The basilica's foundation is bound to the figure of Helena, mother of the emperor Constantine, whose pilgrimage to Jerusalem in the 320s is the origin of the legend of the Finding of the True Cross. According to that tradition she recovered the wood of the cross at Golgotha and brought a share of it, with other relics of the Passion, back to Rome, converting a hall of her Sessorian residence into a chapel to hold them. The relics now displayed in the Chapel of the Relics include three small fragments of wood venerated as the True Cross, one of the nails, two thorns associated with the Crown of Thorns, and part of the cross of the Good Thief.
The Church presents these as objects of devotion whose ultimate authenticity cannot be proven; medieval Europe held so many claimed fragments of the True Cross that critics joked they would build a ship, though modern estimates suggest the surviving pieces would in fact fit within a single cross. What is historically secure is that Santa Croce has been a centre of the cult of the Cross in Rome since late antiquity.