Michigan Press. ISBN 978-0-472-08149-3. Runciman, Steven (1930). A History of the FirstBulgarianEmpire. London: G. Bell & Sons. Templat:BulgarianEmpire
OCLC 75865504. The FirstBulgarianEmpire. Encarta. Diarkibkan daripada yang asal pada 4 December 2007. Dicapai pada 3 March 2007. Hart, Nancy. Bulgarian Art and
Bulgaria. Volume II. FirstBulgarian State] (dalam bahasa Bulgarian). и колектив. София (Sofia): Издателство на БАН (Bulgarian Academy of Sciences Press)
Bulgaria received its first airplane Bleriot XXI, with which on 13 August 1912 Simeon Petrov flew to become the firstBulgarian to pilot an airplane over