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Alessandro collaborated actively with his brother Francesco in his military campaign, and with him he conquered Milan, Alessandria and Pesaro. In 1435, at Fiordimonte, he won the battle in which the riotous Niccolò Fortebraccio was killed. In 1442 at Assisi he commanded the troops besieged by Pope Eugene IV's condottiero Francesco Piccinino. He was forced to leave the city, abandoning the city to ravages and massacres. In 1444 he obtained the lordship of Pesaro by Galeazzo Malatesta. Here he enlarged the Ducal Palace to conform it to the Renaissance standards.
During the Wars in Lombardy in support of Francesco he presided Parma and, in February 1446, he proclaimed himself lord of the city. After Francesco's conquest of the Duchy of Milan, the Peace of Lodi (1454) confirmed him in Parma.
He married Costanza Varano (1428–1447), the daughter of Pietro Gentile I da Varano, on 8 December 1444. She died while bearing Costanzo. The following year he married to Sveva da Montefeltro (1434–1478), daughter of Guidantonio da Montefeltro, count of Urbino. In 1457, fearing a possible conjure of the Malatesta family to regain the seigniory of Pesaro, he obliged her to become a nun in a monastery in the city.
He also had an illegitimate daughter, Ginevra (c. 1440–1507), known as a patron of the visual and literary arts. She married Sante Bentivoglio in 1454 and, after his death, Giovanni II Bentivoglio, duke of Bologna.
- ‘Sfòrza, Alessandro, signore di Pesaro’, Dizionario Biografico degli Italiani.
- ‘Beauty Adorns Virtue: Renaissance Portraits of Women’ Archived 2010-11-09 at the Wayback Machine, National Gallery of Art.