The question who should invest ( appoint ) whom was the subject of a conflict between the Catholic church ( mainly the papacy ) and state ( mainly the Holy Roman Empire ) in the Middle Ages during the so-called lay investiture controversy . The question who should invest ( or more to the point , appoint ) whom was the subject of an epic conflict between the Catholic Church ( mainly papacy ) and state ( mainly the Holy Roman Empire ) in the Middle Ages during the so-called Investiture Controversy .