Among Shepard's theories is that the breakdown in Byzantine-Khazar relations and the shift in Byzantine foreign policy towards allying with the Pechenegs and the Rus against Khazaria was a result of the Khazar conversion to Judaism.
The theory that this Siward is Siward Barn was advocated by Jonathan Shepard and Christine Fell.
Sam Shepard | Jonathan Swift | Jonathan Ross | Goodluck Jonathan | Jonathan Demme | Shepard Fairey | Jonathan Lethem | Jonathan | Jonathan Richman | Jonathan Coulton | Jonathan Safran Foer | Jonathan King | Jonathan Rhys Meyers | Matthew Shepard | Jonathan Zittrain | Jonathan Silverman | Jonathan Nott | Jonathan Kaplan | Jonathan Harris | Jonathan Cain | Jonathan Butler | Jonathan Borofsky | Jonathan Aitken | Jonathan Wells | Jonathan Tweet | Jonathan Pryce | Jonathan Pearce | Jonathan Dimbleby | Jonathan Blow | E. H. Shepard |