The Venetian historians, John Sagorninus, (Chron. Venet. p. 13,) and the doge Andrew Dandolo, (Scriptores Rer. Ital. tom. xii. p. 135,) have preserved this epistle of Gregory. The loss and recovery of Ravenna are mentioned by Paulus Diaconus, (de Gest. Langobard, l. vi. c. 42, 54, in Script. Ital. tom. i. pars i. p. 506, 508;) but our chronologists, Pagi, Muratori, etc., cannot ascertain the date or circumstances