The subject of my paper concerns the iconography of the mysterious relief at Modena (Galleria Museo e Medagliere Estense, inv. 2676) showing a young god in a cosmic egg. The paper is to review the state of research in modern scholarship since 1863, to discuss various attempts at its interpretation, and to propose my own working hypothesis, which links the Modena relief to the Orphic Rhapsodies and the Middle-Platonic passage transmitted by Porphyry of Tyre in his The Cave of the Nymphs 21–29.