Reginald Pole was a prominent opponent of Henry VIII’s break with the Roman Catholic Church. In 1532, he left England after refusing to approve Henry’s annulment of his marriage to Catherine of Aragon, and spent the next few years studying at Padua. While in Italy, he wrote this book Pro ecclesiasticae unitatis defensione (Defence of the unity of the Church). In response to this text, he was appointed a Cardinal by Pope Paul III and became a devout supporter of the Catholic faith in response to the Reformation.

De unitatis conveys Pole’s beliefs regarding the Reformation in England. The text is a vitriolic attack on Henry VIII, declaring that his arguments for the annulment were invalid and placing the blame for the events that had followed squarely on Henry, Anne Boleyn and the arguments made by Richard Sampson, one of the agents appointed by the king to finalise the divorce. The text even went so far as to encourage the Holy Roman Emperor, Charles V and others to depose Henry and restore order. The book was also responsible for furthering views that John Fisher, Bishop of Rochester, and Sir Thomas More were martyrs following their executions the previous year, something that Pole would dedicate further efforts later in life. It concluded in urging Henry to repent.