 The church 's name gave birth to a legend . When Helena ( mother of Constantine the Great ) returned from her trip to the Holy Land , she brought back two stone relics : one from the presentation of Jesus at the Temple and one on which Abraham bound Isaac . The empress wanted to donate the stones to Saint Peter 's Basilica , but when the convoy arrived at the site of the future church the horses ( Italian : cavalli ) refused to move further despite urging ( Italian : scossi ) . A chapel hosting the stones was built , the origin of the church . The most probable reason for the name was the discovery , near the square , of a thigh from a Roman equestrian statue ( coxa caballi in Vulgar Latin ) . 
