The chief source of the smother of language which concealed and still conceals the character of Felice Peretti, however, was the Pope himself. Words gushed from him in a torrent, spontaneous, uncalculated, recklessly emotional, apparently utterly revealing. And yet, revealing almost nothing. Not, one guesses, usually from any intent to deceive but rather because this spate of language gave relief to all those surface impulses which his stern inner concentration prevented from finding an outlet in action. What is hard to find in his recorded words, or in the gossip about him, is any clue to the great ruler who brought peace and order to the papal states and water to Rome. To know Sixtus V one must look at what he did, not what he said.

Garrett Mattingly, The Defeat of the Spanish A…, loc. 125