Toynbee "Guiglielmo Aldobrandesco"
count of Santafiora in the Sienese Maremma [Santafiora]; mentioned by his son Omberto (in Circle I of Purgatory), [Purg. xi. 59]; un gran tosco, [Purg. xi. 58] [Omberto].

According to a Sienese chronicler [Paolo di Tommaso Montauri, Cron. senese, ann. 1227, in L. A. Muratori, RIS, xv, pt. vi, p. 189], Guiglielmo, who was very powerful in Tuscany and was constantly at war with the Sienese, was imprisoned by them for six months in 1227:

In questo anno stette el conte Guiglielmo da Santa Fiore e' stette in prigione VI mesi [in Siena].

Owing to his animosity against the Sienese, Guiglielmo appears to have abandoned the Ghibelline principles of his house, and to have allied himself with the Florentines and Tuscan Guelphs. He was included in the peace which was arranged between Florence and Siena in 1254, and died shortly after. [Aldobrandeschi.] [See esp. G. Ciacci, Gli Aldobrandeschi nella storia e nella Divina Commedia (Roma, 1935).]

©Oxford University Press 1968. From A Dictionary of Proper Names and Notable Matters in the Works of Dante by Paget Toynbee (1968) by permission of Oxford University Press