incursion into Leopoldstadt on 15 May, which made the final assault imminent. One of Frederick's best generals, Hans von Wulfersdorfer, defended the city walls against the king, but he could not work miracles. Although the Viennese defenders occasionally broke out of the castle and set fire to one of the siege towers during the March, the outcome of the siege was ultimately decided by the depletion of supplies. Unable to build up sufficient food reserves as a result of the 1484 campaigns, exacerbated by the start of the winter siege (which made it impossible to sow the fields or build up additional food reserves), the city of 50,000 people faced severe famine by April, and the organisation within the walls began to organise for the opening of the city gates, which took place on 1 June. The Viennese people realized that and negotiated to surrender the inner city to the Hungarian king. They insisted only that their citizens' privileges would be preserved and a guarantee of safe passage. On 1 June, at the head of a column of his soldiers, Matthias entered the heart of Vienna behind its city walls in spectacular triumph. Five days later, the city councillors of Vienna swore an oath of allegiance to their new ruler, who took the title of Prince of Austria after his conquest. Meanwhile, the imperial city did not fare badly under Hungarian rule either, as in exchange for the lost privileges, Matthias granted it several years of tax exemption, granted it its old freedom, and delegated to the Vienna City Council only one of his men, István Szapolyai, the chief captain. Aftermath In the Salzburg Manifesto, Frederick ordered the Austrian states to refuse Matthias's demand for the assembly of a Reichstag. He also put forward that soon-to-be Emperor Maximilian I would come to an aid. According to tradition, that is the origin of A.E.I.O.U., said to be a secret message to all Austrian provinces. At the end of the campaign, Hungary controlled all of Upper Austria as well, which remained under his control until his death, in 1490. Administrative issues Matthias deprived Vienna of its staple right, which had so much violated the commercial interests of the nearby countries so much that they formed the Visegrád Group to secure a bypass route away from the city. Vienna enjoyed tax exemption under Matthias' rule. He also delegated a member, Stephen Zápolya, to