The splendid Rotunda church in Thessaloniki is the most important monument of the early Christian era. In this comprehensive monograph, Hjalmar Torp presents the findings of his life-long archaeological and iconographic research on the Rotunda. He explores the archaeological data, the architectural phases and the chronological problems of the monument. The nuanced descriptions of the mosaics, their colours and technique, are the result of close examination from scaffolding. On this basis, the iconography of the mosaics is analysed and interpreted in conjunction with historical and theological sources. The execution of the palatine church and its sumptuous decoration is attributed to the initiative of the emperor Theodosius the Great. This edition, abundantly documented and richly illustrated is a unique tribute to the Rotunda.