Pope Leo IV served as the head of the Roman Catholic Church from 847 to 855. He is best known for his efforts to strengthen the papacy and protect Rome from external threats, particularly from the Saracens. Leo IV initiated the construction of the Leonine City, a fortified area around the Vatican, to enhance the city's defenses. During his papacy, Leo IV also focused on church reforms and the promotion of education. He convened synods to address various issues within the church and worked to improve the moral standards of the clergy. His leadership helped to stabilize the papacy during a tumultuous period in history.