"Carlow Castle". Carlow Town.com. Arkiveret fra originalen 17. november 2007. Hentet 9. december 2007.
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books.google.be
Crouch p.226 writes: "From his earliest appearances in the History, William son of John Marshal is invariably William li Mareschal, or often just li Mareschal."
livingthehistoryelizabethchadwick.blogspot.co.uk
Chadwick, Elizabeth (11. oktober 2009). "Biography of John Marshall". livingthehistoryelizabethchadwick.blogspot.co.uk.
usna.edu
Abels, Dr. Richard. Medieval Chivalry, The United States Naval Academy. Accessed 8 February 2012.
web.archive.org
"Carlow Castle". Carlow Town.com. Arkiveret fra originalen 17. november 2007. Hentet 9. december 2007.