Marriage proposals
When the House of Sforza was restored to the Duchy of Milan in 1512, Isabella hoped to wed Bona and Duke Maximilian Sforza, thereby providing further legitimacy to Maximilian's reign. There were other proposals as well: Spanish King Ferdinand II of Aragon proposed Giuliano de' Medici, brother of Pope Leo X. Isabella counter-proposed Ferdinand's 10-year-old grandson Ferdinand of Austria; Pope Leo X proposed Philippe, Duke of Nemours, who would succeed to the Duchy of Savoy if his brother Charles III abdicated. The initial and most likely plan to marry Maximilian Sforza failed after he was deposed after the French victory in the Battle of Marignano in 1515. Pope Leo X proposed his nephew Lorenzo de' Medici, Duke of Urbino, as he hoped to install Lorenzo as Duke of Milan by using Bona's inheritance claims. However, the French hold on Milan was too strong and the plan failed.
After Polish King Sigismund I the Old was widowed in October 1515, Maximilian I, Holy Roman Emperor did not want Sigismund to marry another Habsburg opponent like his late wife, Barbara Zápolya. Therefore, the Emperor acted quickly and selected three suitable candidates for Sigismund: his granddaughter Eleanor of Austria, widowed Queen Joanna of Castile, and Bona Sforza. Although 36-year-old Joanna was eliminated because of her age, and Eleanor's older brother instead selected King Manuel I of Portugal for her husband, Polish nobles suggested Anna Radziwiłł, the widow of Konrad III of Masovia. Isabella sent Bona's old teacher, Crisostomo Colonna, and diplomat Sigismund von Herberstein to Vilnius to convince Sigismund to select Bona. They succeeded and the marriage treaty was signed in September 1517 in Vienna. Bona's dowry was very large: 100,000 ducats, personal items worth 50,000 ducats and the Duchy of Bari. In exchange, Sigismund granted his future wife the towns of Nowy Korczyn, Wiślica, Żarnów, Radomsko, Jedlnia, Kozienice, Chęciny, and Inowrocław.
Jan Konarski, Archbishop of Kraków, travelled to Bari to bring Bona to Poland. The wedding per procura took place on 6 December 1517 in Naples. Bona wore a dress of light blue Venetian satin that reportedly cost 7,000 ducats. The journey to Poland took more than three months. Bona and Sigismund met for the first time on 15 April 1518 just outside Kraków.