The city was invaded on 24 May 1823 by a French army—the so-called Hundred Thousand Sons of Saint Louis—called to intervene to restore the absolutism of Ferdinand that the latter had been deprived from during the 1820–1823 "trienio liberal". Unlike other European capitals, during the first half of the 19th century the only noticeable bourgeois elements in Madrid (that experienced a delay in its industrial development up to that point) were merchants. The University of Alcalá de Henares was relocated to Madrid in 1836, becoming the Central University.