Louis XI of France at once seized the Duchy of Burgundy, which was ever afterwards a part of the French dominion. The County of Burgundy with the Netherlands remained under Mary's rule. The towns were not slow in reasserting their rights and recovering the privileges that had been wrested from them by the Burgundian princes. Mary married Maximilian of Austria, son of the Emperor Frederick III, and at her death, a few years later, left two children, Philip the Fair and Margaret of Austria. Philip espoused Joanna, daughter of Ferdinand and Isabella of Castile and Aragon, and became the father of Charles V. Then began that unfortunate connection with Spain which brought such misery to the Low Countries. Charles, who not only ruled the Netherlands and Austria, but was elected Emperor and King of Spain, governed his provinces of the Low Countries with despotic sway. At one time the Ghenters incurred his wrath by rising against the payment of a war tax and even carrying on secret negotiations with Francis I, Charles's great rival. Francis basely betrayed them to Charles, who took possession of the city with a large army. Their leaders were beheaded, many citizens were exiled, and the guild chiefs and members of the council were brought before the Emperor with halters about their necks and forced to sue for pardon. Henceforth no magistrate of Ghent was allowed to appear in public without wearing the halter. This sign of submission became the badge of the town, but in later years it was made of silk and worn as a decoration. The city lost its privileges and its great bell, Roland. At this time, too, the enormous citadel, called the Spaniards' Castle, was erected at Ghent by Charles's orders. The garrison of this stronghold was often, during the Spanish occupation of the country, of service in suppressing insurrections in Flanders. The Low Countries had never been more prosperous than at the accession of Philip II. With the vast increase in commerce had come great wealth and unexampled luxury. Antwerp, which held the place formerly belonging to Bruges, was the richest city in Northern Europe. It was said as much business was done on the exchange of Antwerp in one month as on that of Venice in two years. Under the Burgundians music, architecture, painting, lace-making and tapestry were all brought to great perfection, and the University of Louvain was founded. One important advance in government under Charles V must be noted. A code of laws was formed from the customs that had grown up under the charters of the towns and the proclamations of the rulers.