This article aims to shed light upon the Early Byzantine cult of relics by exploring the origins and development of one of its most prevalent surviving artefacts, the marble sarcophagus reliquary. Evidence from a range of sources will be considered, from contemporary and near-contemporary texts, through archaeological studies and ancient artefacts, to the use of modern scientific research. The following questions are thus explored: how and where were sarcophagus reliquaries developed, produced, and circulated, how were they used and by whom? This paper will propose that the sarcophagus reliquary was developed primarily at Constantinople for use by the imperial elite, in connection with the contemporary rise of the cult of relics. Like other elements of church furniture, it became part of a commercial production, primarily in Proconnesian marble, and was exported across the Adriatic and eastern Mediterranean, particularly to areas with close connections to the imperial capital.