Pope Benedict XVI on Thursday made his most important change yet in the Vatican hierarchy, placing in the church’s No. 2 spot a conservative cardinal who once tried to lead a boycott of the controversial novel “The Da Vinci Code.”

The Vatican announced the appointment of Italian Cardinal Tarcisio Bertone, of Genoa, as secretary of state, a position roughly equivalent to that of prime minister. He will succeed Cardinal Angelo Sodano, 78, who served in the post for 15 years and became especially powerful as the health of the late Pope John Paul II deteriorated.