In the eighteenth century, two French travelers to Spanish Naples noted that “the real leader of the Neapolitans was neither the viceroy nor the king; he could be found in a vial in a bronze tabernacle with silver doors in a magnificent chapel of the cathedral: it was San Gennaro.”3 Who was this spiritual leader who dominated Naples? Martyred in the fourth century, San Gennaro is Naples’ major saint. Gennaro’s preserved blood liquefied each time it was put in contact with its relics. This liquefaction was called the “miracle of the blood” and the community perceived this phenomenon as a good omen for the city. However, the belief that San Gennaro’s blood validated the power of its proprietor created numerous power struggles. In fact, since ancient times, whoever controlled the relics, and therefore the miracle of the blood, controlled politics in Naples. This chapter examines how the disputes over holy power associated with the blood created space for the Spanish viceroys. As people believed that the saint granted favors when he bled, these imperial officers capitalized on the struggle over the miracle of the saint’s ceremony.