Saint Peter Nolasco's Vision of Saint Peter the Apostle
It shows Peter the Apostle crucified upside-down appearing to Peter Nolasco , founder of the Order of the Blessed Virgin Mary of Mercy , which redeemed Christian slaves from Muslim owners during the Reconquista period in Spanish history . 
<triplet> Peter Nolasco <subj> Order of the Blessed Virgin Mary of Mercy <obj> religious order <triplet> Order of the Blessed Virgin Mary of Mercy <subj> Peter Nolasco <obj> founded by