Note AXX
Extra note by the Rev. H. H. Milman
1782 (Written), 1845 (Revised)
It should be Pope Martin the Fifth. See Gibbon's own note, ch. lxv, note 51 and Hobhouse, Illustrations of Childe Harold, p. 155.
The History Of The Decline And Fall Of The Roman Empire Fall In The EastChapter 71