Who Excommunicated Whom and with What Authority?

It remains a point of dispute in discussions of the supposed and so-called schism between East and West as to whether Cardinal Humbert, as papal legate, actually had authority to excommunicate the Ecumenical Patriarch in 1054 during their famously mutual temper tantrum in Constantinople. Perhaps this new book, forthcoming in November, will shed light on this vexed and significant issue--though, of course, even if it does, it will change little insofar as (a) the excommunications were officially "lifted" in December 1965 by Pope Paul VI and Patriarch Athenagoras; and (b) the real issues are not juridical and never have been: Kriston Rennie, The Foundations of Medieval Papal Legation (Palgrave Macmillan, 2013), 264pp.

About this book we are told:

As the pope's alter ego, the medieval papal legate was the crucial connecting link between Rome and the Christian provinces. Commissioned with varying degrees of papal authority and jurisdiction, these hand-picked representatives of the Roman Church were nothing less than the administrative, legal, and institutional embodiment of papal justice, diplomacy, government, and law during the Middle Ages. By examining the origins and development of this ecclesiastical office in the early Middle Ages, this book defines the papacy's early contribution to medieval European law and society.
Presenting a pioneering inquiry into the field, The Foundations of Medieval Papal Legation demonstrates the growth of papal government and its increasing reliance on representation beyond Rome, explaining how this centralized position was achieved over time, going further to legitimize the papacy's burgeoning need for increased supervision, mediation, and communication throughout western Christendom. In so doing, it contributes to a wider administrative, legal, and institutional understanding of papal government in early medieval Europe as a whole.