Taddeo d'Este (ca. 1390 – 21 June 1448) was a condottiere, a freelance military leader, who was known for his defense of the Republic of Venice in 1439 against Milanese forces under Niccolò Piccinino. Unlike many other condottieri of the day, who often changed sides, he served Venice almost exclusively throughout his thirty-year military career. During most of this period Venice was constantly at war with one or more of the neighboring states in northern Italy. Early years Taddeo d'Este was born around the last decade of the fourteenth century in Este, the second son of Obizzo II d'Este, of the younger branch of the family that ruled Ferrara. His mother belonged to the noble family of Collalto. Taddeo became a mercenary at an early age, fighting for Venice, and gave the republic his loyalty for the next thirty years during the wars in which the city struggled to gain territory in the Terraferma, on the mainland. However, he was never given independent command for any length of time. Friuli and Istria 1414–1422 Taddeo d'Este was active in the struggle for territory between Venice and the Patriarch of Aquileia. In 1414 Taddeo led a squad of fifteen lances (cavalrymen) in a fight at Zadar against the armies of Sigismund of Luxembourg. The next year he was given permission to return to Este to look after family affairs, since his father had just died. When the truce with Sigismund broke down, in April 1417 he was sent back at the head of 50 lances. In September 1418 he was leading a force of 70 lances in the village of Brugnera, a defensive position along the Treviso-Udine line. In November 1419, with 100 horsemen, he was sent to defend Cividale del Friuli against Hungarian troops under Louis of Teck, the Patriarch of Aquileia. He organized the defense successfully, then managed to break out and defeat the Hungarians in open battle. By the end of the month he was able to raise the Venetian banner over the castles of Gorizia and Duino. By June 1420 most of Friuli had been conquered and another truce had been arranged with Sigismund. Taddeo returned on leave to Venice and in September married Magdalene, daughter of Filippo Arcelli, governor general of the Friuli army. He was required to return to Friuli immediately after his marriage. In January 1421 he was dispatched to Istria. When Arcelli became ill