Lives and Times of the Popes: Leo IV - Biography. From the book by Alexis François Artaud de Montor. www.saint-mike.org/Library/Papal_Library/LeoIV/biography.html
Pope Leo IV - Illustrated profile. www.catholic-forum.com/saints/saintl25.htm
Pope St. Leo IV - Biographical article on this Roman, who died in 855. From the Catholic Encyclopedia. www.newadvent.org/cathen/09159a.htm
St. Leo IV - Brief account of his pontificate. From the book "Popes Through the Ages," by Joseph Brusher. www.cfpeople.org/Books/Pope/POPEp104.htm
The Ecole Glossary: Leo IV - Brief biography, by Karen Rae Keck. cedar.evansville.edu/~ecoleweb/glossary/leoiv.html
