Greco-Roman religion in the ancient Mediterranean permeated aspects of everyday life, including seafaring. Besides cargo, ships transported mariners' religious beliefs from port to port, thus disseminating religious culture. Shipboard ritual, however, remains largely inferred from Latin and Greek texts, iconography, and isolated archaeological finds. Several accounts record that tutelary statues were carried on board to deliver a ship from peril. These accounts are supported by iconographic representations of deities on the hull and a relief scene which shows the use of altars and incense in shipboard ritual. Moreover, ritual objects, including altars, small statuary, incense burners, and lustral basins, have been found among shipwrecks, but prior archaeological research has been particularistic, singling out ritual objects in shipwrecks. Their presence, however, does not necessitate shipboard ritual since these items may have been cargo. To distinguish between personal items and cargo on board ancient shipwrecks, I analyze such objects both objectively and subjectively: first focusing on an object to discern a potential purpose and then again within a spatial context to define its actual purpose. Additionally, I develop religious and social space theories for shipboard analysis, identifying ritual at the bow and stern and concluding that the stern in particular served as an axis mundi, a central location for divine communication. Furthermore, because of this comprehensive approach, large ritual objects such as altars and lustral basins often can be identified primarily as cargo. Ultimately, applying social space theory to shipwrecks can redefine our interpretation of religious activity on board the ship, an intermediary in the dissemination of culture.