Leo IV, Saint, pope d. 855, pope (847–55), a Roman; successor of Sergius II. He had seen the Saracen attack on Rome (846), and to prevent its recurrence he fortified the city and its suburbs. He built a wall around the Vatican, established and fortified the part of Rome still called the Leonine City, and rebuilt churches. He crowned Louis II Holy Roman emperor. Leo was succeeded by Benedict III. Feast: July 17.

The Columbia Encyclopedia, Sixth Edition. Copyright © 2001 Columbia University Press.