On February 24, 1530, on his thirtieth birthday, Charles V was crowned Emperor of the Holy Roman Empire by Pope Clement VII in the San Petronio Basilica in Bologna. The coronation was a watershed moment in Imperial– Papal relations, following the nadir of the Sack of Rome in 1527 and eventual rapprochement after the conclusion of the Treaty of Cambrai in August 1529. In the following months, Clement VII negotiated the restoration of his Medici relatives to Florence and, in exchange, agreed to crown Charles in Rome. Charles must have imagined a splendid coronation at St Peters Basilica followed by a triumphant descent to Naples to celebrate his rule. However, such plans came to nought. In late September 1529, Suleiman I attacked the city of Vienna with over 100,000 soldiers in a two-and-a-half-week-long siege. Although the Habsburg stronghold withstood the Ottoman attack, the damage to imperial resolve was palpable. Charles V moved the coronation to the northern city of Bologna, so that he, and his troops, could move quickly to central Europe if necessary to assist his brother, Ferdinand. However, before travelling to Vienna, he spent a month in Mantua in the company of Federico Gonzaga, who lavished his important guest with sumptuous banquets, excellent hunting expeditions, and visits to the famed Palazzo Te.