Guerri.

The Guerri descend from the Conti Guidi, one of the greatest feudal houses of medieval Tuscany: Counts of Modigliana from 925 with Tegrimo I († c. 930) and, through Tegrimo VI (c. 1175 – c. 1234), Counts of Porciano and Counts Palatine.

Among the descendants of Tegrimo VI, Guido «Zeffiro», Count of Val d'Ambra († c. 1348), and his son Giovanni († 1363) lose all their goods in 1336 to the benefit of the Republic of Florence. Giovanni's son, Pietro, then moves to Siena: there he loses his noble rank and must take a surname to be counted among the citizens of Siena and gain access to public offices. In the documents he appears under various spellings — Guerra, Guerrae, de Guerris, Guerri — whence the definitive patronymic Guerri.

At Siena the Guerri obtain admission to the city patriciate thanks to the high public offices held by some of their members (thus Nanni di Pietro di Giovanni Guerri, 1445, State Archives of Siena). The family, of ancient Tuscan tradition, counted among its members notaries, magistrates and men-at-arms, recorded in the archives of the Republic of Siena and, later, of the Grand Duchy of Tuscany.

The arms of the Guerri preserve the white-and-green bichromy of the Conti Guidi, with a Ghibelline partition (vert a bend argent), accompanied by six mullets or added in the 16th century as a noble mark. They are found in the first and fourth quarters of the quartered shield of the house of Guerri dall'Oro, beside that of the dall'Oro.

A collateral branch of the Guerri, having moved to Venice, obtained the title of Count and admission to the Libro d'Oro of the titled families of the Serenissima. It is a documented cousin line, distinct from the family's direct line, to which the entry Venetian Patriciate is devoted.

The direct line documented at Siena continues over several generations down to Pietro Giovanni Guerri (1819–1880), an officer at the Grand-Ducal Court of Tuscany, who in 1862 marries Dejanira dall'Oro (1835–1900), the last of her House, adding his wife's surname to his own.

Thus is born the double surname Guerri dall'Oro, which unites the Tuscan tradition of the Guerri with the Venetian one of the dall'Oro and continues today in the Princes of Tricase.