In reality, coins of Maximus son Flavius Victor sometimes depict a tower on the reverse, but whether this inspired the legend about the castles his father built is unknown. Coin of Flavius Victor.
Haycock, Marged «Early and Medieval Literature». The Year's Work in Modern Language Studies, 51, 1989, pàg. 549–552. JSTOR: 20868237.
Frazer, J. G.. “Notes on Welsh Folk-Lore.” folklore, vol. 4, 1893, pp. 122-123, Taylor & Francis, Ltd. on behalf of Folklore Enterprises, Ltd., https://www.jstor.org/stable/1253223.