Sir: You report ("Anglican service hears Muslim preacher's plea", 20 May) that a Muslim has preached in the chapel of Selwyn College, Cambridge, on the common ground between Muslims and Christians. This prompts me to acquaint your readers with a letter written in 1076 in the same spirit, by Pope Gregory VII. To a Muslim king in North Africa he wrote:
Your people and ours owe each other a debt of mutual charity, beyond even the debt we owe to all peoples, since both of us believe in and worship the same God, albeit in different ways.
The king had shown tolerance and encouragement to his Christian subjects, released prisoners, and sent a candidate for ordination as their bishop, acts which, Gregory said, were clearly divinely inspired.
Alas, only 15 months earlier Gregory had felt compelled to write to the Christian Emperor in Germany with news of "unheard-of slaughter" of Christians in the Byzantine empire, slaughter which, the Pope feared, might annihilate Christendom altogether in those "overseas" parts.
The facts were that in 1071 the Seljuk Turks, relative newcomers to Islam, had understood its message in more militant terms, and invaded and conquered most of Byzantium's Asian "home counties" (in what is now Turkey). There was no assurance at all that Byzantium itself would hold out. So Gregory's letter to the German emperor urged co-operation in a major military expedition to the East.
Domestic troubles held up the expedition for 20 years, but it resurfaced in 1095 as the first crusade. There seems to be a lesson in these events.
Tutor in Medieval History