E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Sagan of Jerusalem,
in Drydens Absalom and Achitophel, is designed for Dr. Compton, Bishop of London; he was son of the Earl of Northampton, who fell in the royal cause at the battle of Hopton Heath. The Jewish sagan was the vicar of the sovereign pontiff. According to tradition. Moses was Aarons sagan.
The Sagan was the vicar of the Jewish pontiff. Thus they called Moses Aarons Sagan.