Frederick III

Frederick III adopted the motto AEIOU, which he used extensively on buildings and documents. The meaning of the acronym is uncertain, but it is often interpreted as 'Austriae est imperare orbi universo' (It is Austria's destiny to rule the world). This motto reflected Frederick's long-term vision for Habsburg dominance.

Frederick III was crowned Holy Roman Emperor by Pope Nicholas V in Rome, the last emperor to be crowned in the city. His coronation reaffirmed the traditional alliance between the Empire and the Papacy. Frederick's long reign (53 years) was the longest of any Holy Roman Emperor.

Frederick III signed the Treaty of Wiener Neustadt with his brother Albert VI, ending a conflict over the Habsburg inheritance. The treaty divided the Habsburg lands, with Frederick retaining control of Austria and Albert receiving parts of Further Austria. This agreement temporarily stabilized the internal Habsburg situation.

Frederick III arranged the marriage of his son Maximilian I to Mary of Burgundy, heiress of the Burgundian state. This marriage brought the wealthy Burgundian territories, including the Netherlands, into the Habsburg orbit. It was a cornerstone of Habsburg power and led to centuries of conflict with France.

Frederick III was besieged in Vienna by the forces of Matthias Corvinus, King of Hungary. After a prolonged siege, Frederick was forced to flee the city, which fell to Corvinus. Frederick spent the next years in exile in Graz, unable to reclaim his capital until Corvinus's death in 1490.