Gren 2002, p. 110: "Something of it, though, has been saved for posterity in the extracts made later by the Greek Byzantine patriarch Photios..." Gren, Erik (2002). Orientalia Suecana, Volumes 51–52. Stockholm, Sweden: Almquist & Wiksell Periodical Company.
Mango 1980, pp. 168–169; Treadgold 1983, p. 1100. Mango, Cyril A. (1980). Byzantium: The Empire of New Rome. New York, NY: Charles Scribner's Sons. ISBN0-684-16768-9. Treadgold, Warren T. (October 1983). "Review: Patriarch Photios of Constantinople: His Life, Scholarly Contributions, and Correspondence together with a Translation of Fifty-Two of His Letters by Despina Stratoudaki White; The Patriarch and the Prince: The Letter of Patriarch Photios of Constantinople to Khan Boris of Bulgaria by Despina Stratoudaki White; Joseph R. Berrigan, Jr". Speculum. 58 (4). Medieval Academy of America: 1100–1102. doi:10.2307/2853829. JSTOR2853829.
Bougard, Francois (2002). "Hadrian III". In Levillain, Philippe; O'Malley, John W. (eds.). The Papacy: Gaius-Proxies. Psychology Press. p. 682. ISBN978-0-415-92230-2. Retrieved 25 March 2024.
Treadgold 1983, p. 1100 Treadgold, Warren T. (October 1983). "Review: Patriarch Photios of Constantinople: His Life, Scholarly Contributions, and Correspondence together with a Translation of Fifty-Two of His Letters by Despina Stratoudaki White; The Patriarch and the Prince: The Letter of Patriarch Photios of Constantinople to Khan Boris of Bulgaria by Despina Stratoudaki White; Joseph R. Berrigan, Jr". Speculum. 58 (4). Medieval Academy of America: 1100–1102. doi:10.2307/2853829. JSTOR2853829.
Mango 1980, pp. 168–169; Treadgold 1983, p. 1100. Mango, Cyril A. (1980). Byzantium: The Empire of New Rome. New York, NY: Charles Scribner's Sons. ISBN0-684-16768-9. Treadgold, Warren T. (October 1983). "Review: Patriarch Photios of Constantinople: His Life, Scholarly Contributions, and Correspondence together with a Translation of Fifty-Two of His Letters by Despina Stratoudaki White; The Patriarch and the Prince: The Letter of Patriarch Photios of Constantinople to Khan Boris of Bulgaria by Despina Stratoudaki White; Joseph R. Berrigan, Jr". Speculum. 58 (4). Medieval Academy of America: 1100–1102. doi:10.2307/2853829. JSTOR2853829.
Treadgold 1983, p. 1100 Treadgold, Warren T. (October 1983). "Review: Patriarch Photios of Constantinople: His Life, Scholarly Contributions, and Correspondence together with a Translation of Fifty-Two of His Letters by Despina Stratoudaki White; The Patriarch and the Prince: The Letter of Patriarch Photios of Constantinople to Khan Boris of Bulgaria by Despina Stratoudaki White; Joseph R. Berrigan, Jr". Speculum. 58 (4). Medieval Academy of America: 1100–1102. doi:10.2307/2853829. JSTOR2853829.
Mango 1980, pp. 168–169; Treadgold 1983, p. 1100. Mango, Cyril A. (1980). Byzantium: The Empire of New Rome. New York, NY: Charles Scribner's Sons. ISBN0-684-16768-9. Treadgold, Warren T. (October 1983). "Review: Patriarch Photios of Constantinople: His Life, Scholarly Contributions, and Correspondence together with a Translation of Fifty-Two of His Letters by Despina Stratoudaki White; The Patriarch and the Prince: The Letter of Patriarch Photios of Constantinople to Khan Boris of Bulgaria by Despina Stratoudaki White; Joseph R. Berrigan, Jr". Speculum. 58 (4). Medieval Academy of America: 1100–1102. doi:10.2307/2853829. JSTOR2853829.
