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Destined for an ecclesiastical career, Zeno studied at Padua, but dedicated himself instead to pursuing women and the good life. He thus ran out of money and enlisted in a band of mercenaries, returning to Venice after four or five years.
While at Patras, the city was attacked by Turkish forces. Zeno distinguished himself in battle, but later made himself a hunted man after he killed a Christian knight with whom he had had an argument. He traveled to Constantinople, was married, and lived like a merchant. He was at Tenedos, a Venetian possession, when it was attacked by the Genoese. As the bailiff and captain of Negropont, Zeno found himself in command of eighteen galleys, which he employed in raiding expeditions in the Mediterranean.
Carlo Zeno had long since been ordered to return to Venice, but the slowness and difficulty of communication and movement under 14th century conditions delayed his reappearance. He returned to Venice with this fleet on January 1, 1380, just in time to save the city in the pivotal Battle of Chioggia. The battle took place in June 1380 in the lagoon off Chioggia, resulting in a victory for Venice. The Genoese surrender allowed the Venetians to regain control of the Adriatic.
In 1400, he was considered as a candidate for the office of doge, but Michele Steno was elected instead. In 1404, as commander of the Venetian army, he failed to march against Padua and was jailed for a year. His career compromised, from 1405 Zeno traveled throughout the Mediterranean as a mercenary-for-hire and married again (he was thrice widowed). He returned to Venice aging and infirm and died in 1418.