This episode is set in 1192, at the end of the Third Crusade (1189-1192), which was sanctioned by Pope Gregory VIII (why Robin refers to it as 'Pope Gregory's' war). During this campaign, King Richard I of England - also known as Richard the Lionheart - fought against the infidel hordes. As Richard was absent from the country, he had appointed the Bishop of Ely as his justiciar (or regent).
Richard's brother Prince John - mentioned by Sir Edward as the man who 'gives out the Shires'- allegedly attempted to overthrow the Bishop and seize power for himself. However, when Richard returned from the crusades in 1194, after being captured and imprisoned, he forgave his brother and named him heir to the throne.