A native of Bologna, Spada studied in the Academy of the Carracci brothers, but later left for Rome and became identified with the followers of Caravaggio. This painting would seem to be based on a lost work by Caravaggio himself, intended for the Church of Santa Maria del Popolo but rejected by the client. Subjects from the life of the patron of the Eternal City, the Apostle Peter, were very popular in Roman art. The Pope, head of the Catholic Church, is seen as St Peter's deputy on earth. According to legend, Peter was martyred on the Vatican Hill, crucified upside down by unbelievers. Spada shows the moment when the cross is erected: the uneven balance of the composition is emphasised by sharp contrasts of light and shade. With cold objectivity the artist depicts the tortured body of the elderly apostle and the business-like energy of the murderers.