Ferdinand, however, had not abandoned his reactionary goals, and appealed to the Holy Alliance established at the Congress of Vienna in 1814, by which the main absolutist monarchies of Europe had agreed to help each other in case one of them had to suffer a democratic revolution. On 7 April 1823, France launched an expedition, by which a military corps, known as the One Hundred Thousand Sons of St. Louis "(Los Cien Mil Hijos de San Luis)" and led by Louis Antoine, Duke of Angoulême, invaded the Spanish territory. Louis was welcomed on 24 May in Madrid, after the liberals had abandoned the city and taken refuge in the commercial city of Cádiz, where Ferdinand was kept as prisoner.