I came across the Rus Khaganate's 860 Siege of Constantinople at en.wikipedia.org/wiki/Siege_of_ ... nople_(860
The historical record isn't quite clear why they retreated. Later stories suggest that praying to the icon of Mary helped.
However, Jerbiton belonged to a group of magicians known as the League of Thebes. Is it possible that they may have rallied to the defense of Constantinople?
IIRC Constantinople was not really threatened by this 'siege'. The city proper was surprised, but reasonably well protected by the Theodosian Walls: so what really happened was the sack of its suburbs.
Byzantine sources of the 9th century have Emperor Michael III hurriedly returning with his army from a war against the Arabs, entering the city and repelling the 'siege' - but at that time the Rus might have just as well already retreated with their booty on their own volition.
Jerbiton died in the 830s, but the League of Iconophiles still exists 860, and hence might well have reacted to the Rus' invasion. The issue should be mentioned in sub rosa #16 865 AD: Voventes Centennales.
Cheers
Just realised that I made a total noob error. I got the 800's mixed up with the 8th century when the Order of Hermes was founded.
Apologies.