During his patronage of the Visconti Castle, he contributed to the growth of the collection of scientific treatises and richly illuminated manuscripts in the Visconti Library. Gian Galeazzo was the son of Galeazzo II Visconti and Bianca of Savoy. His father possessed the signoria of the city of Pavia. In 1385 Gian Galeazzo gained control of Milan by overthrowing his uncle Bernabò through treacherous means by faking a religious conversion and ambushing him during a religious procession in Milan. He imprisoned his uncle who soon died, supposedly poisoned on his orders.
Marriage and issue
His first marriage was to Isabelle of Valois, who brought him the title of comte de Vertus in Champagne, rendered in Italian as Conte di Virtù, the title by which he was known in his early career. They had:
After Galeazzo's wife Isabelle died in childbirth in 1373, he married secondly, on 2 October 1380, his first cousin Caterina Visconti, daughter of Bernabò; with her he had:
Gian Maria
Filippo Maria
Conflict with France
Galeazzo was a devoted father to his daughter Valentina. He reacted to gossip about Valentina at the French Court by threatening to declare war on France. The wife of King Charles VI of France was Isabeau of Bavaria, the granddaughter of Bernabò Visconti, and, thus, a bitter rival of Valentina and her father Gian Galeazzo Visconti. Galeazzo's role as a statesman also took other forms. Soon after seizing Milan he took Verona, Vicenza, and Padua, establishing himself as Signore of each, and soon controlled almost the entire valley of the Po, including Piacenza where in 1393 he gave the feudal power to Confalonieri Family on the lands they already had in the valleys around Piacenza. He lost Padua in 1390, when it reverted to Francesco Novello da Carrara. He received the title of Duke of Milan from Wenceslaus, King of the Romans in 1395 for 100,000 florins. In 1396, after the disaster of Nicopolis, Galeazzo was strongly suspected of having informed the Ottomans of the crusaders' plans and of the size and strength of their army as vengeance for his daughter being accused of being behind the illness of King Charles VI of France, and for France's increasing control over the city of Genoa that he had attempted to hamper, for which he had been rebuked by Enguerrand VII de Coucy before the battle. In 1400, Gian Galeazzo appointed a host of clerks and departments entrusted with improving the public health. For the new system of administration and bookkeeping this established, he is credited with creating the first modern bureaucracy, with the assistance of his Chancellor Francesco Barbavara.
Uniting Italy
Gian Galeazzo had dreams of uniting all of northern Italy into one kingdom, a revived Lombard empire. Obstacles included Bologna and especially Florence. In 1402, Gian Galeazzo launched assaults upon these cities. The warfare was extremely costly on both sides, but it was universally believed the Milanese would emerge victorious. The Florentine leaders, especially the chancellor Coluccio Salutati worked successfully to rally the people of Florence, but the Florentines were being taxed hard by famine, disease, and poverty. Galeazzo won another victory over the Bolognese at the Battle of Casalecchio on 26 June 1402. Galeazzo's dreams were to come to naught, however, as he succumbed to a fever at the castello of Melegnano on 10 August 1402. He died on 3 September. His empire fragmented as infighting among his successors wrecked Milan, partly through his division of his lands among both legitimate and illegitimate children. Gian Galeazzo spent 300,000 golden florins in attempting to turn from their courses the rivers Mincio from Mantua and the Brenta from Padua, in order to render those cities helpless before the force of his arms. Notable are his library, housed in the grandest princely dwelling in Italy, the castello in Pavia, and his rich collection of manuscripts, many of them the fruits of his conquests. Furious at French political maneuvering that had removed Genoa from his influence, Gian Galeazzo had been attempting to stop the transfer of Genoese sovereignty to France and Coucy was dispatched to warn him that France would consider further interference a hostile act. The quarrel was more than political. Valentina Visconti, the wife of the Duke of Orleans and Gian Galeazzo's beloved daughter, had been exiled from Paris due the machinations of Queen Isabeau the same month as the departure of the crusade. The Duke of Milan threatened to send knights to defend his daughter's honor but, in the wake of the disaster at Nicopolis, it was widely believed that he had relayed intelligence to Bayezid I of crusader troop movements. There is no firm evidence of this and it is likely that Gian Galeazzo became a scapegoat after the fact due the existing animosity with France, though there remains the possibility that the Duke of Milan, who had murdered his own uncle to ensure his own power, did in fact betray the crusaders. Coucy, his diplomatic mission complete and accompanied by Henry of Bar and their followers, left Milan for Venice, from where he requisitioned a ship on 17 May to take him across the Adriatic Sea, landing in the Croatian port of Senj on 30 May before making his way overland to the rendezvous in Buda.
