It is built of brick cased in marble from the quarries which Gian Galeazzo Visconti gave in perpetuity to the cathedral chapter.
Galeazzo left a son, Gian Galeazzo, who became sole lord of Milan by seizing and imprisoning his uncle Bernabo.
He subsequently spent a long, suspicious, secret and incomprehensible career in the attempt to piece together Gian Galeazzos Lombard state, and to carry out his schemes of Italian conquest.
Soon after that prince had firmly established his power as nominal guardian and protector of his nephew Gian Galeazzo but really as usurping ruler of the state, he revived a project previously mooted for the erection of an equestrian monument in honour of the founder of his house's greatness, Francesco Sforza, and consulted Lorenzo dei Medici on the choice of an artist.
In that year the long ousted and secluded prince, Gian Galeazzo, died under circumstances more than suspicious.
In 1413 Ladislas attacked the papal states once more, driving John from Rome, and threatened Florence; but like Henry VII., Gian Galeazzo Visconti, and other enemies of the republic, he too died most opportunely (6th of August 1414).
The tyrants of Milan were aspiring to royal alliances; Gian Galeazzo Visconti had been married to Isabella of France; Violante Visconti, a few years later, was wedded to the English duke of Clarence.
Internal disorders broke out, and Gian Antonio Orsini, prince of Taranto, led a revolt against Joanna in Apulia; Louis of Anjou died while conducting a campaign against the rebels (1434), and Joanna herself died on the 11th of February 1435, after having appointed his son Rene her successor.
He hoped to secure this duchy for his son, Don Carlos; and Elisabetta further brought with her a claim to the grand-duchy of Tuscany, which would soon become vacant by the death of Gian Gaston.e de Medici.
Thus was elaborated the type of despot which attained completeness in Gian Galeazzo Visconti and Lorenzo de Medici.