Riga has one of the largest collections of Art Nouveau buildings in the world, with at least 800 buildings. This is due to the fact that at the end of the 19th and beginning of the 20th centuries, when Art Nouveau was at the height of its popularity, Riga experienced an unprecedented financial and demographic boom. In the period from 1857 its population grew from 282,000 (256,200 in Riga itself and another 26,200 inhabitants beyond the city limits in patrimonial district and military town of Ust-Dvinsk) to 472,100 in 1913. The middle class of Riga used their acquired wealth to build imposing apartment blocks outside the former city walls. Local architects, mostly graduates of Riga Technical University, adopted current European movements and in particular Art Nouveau. Between 1910 and 1913, between 300 and 500 new buildings were built each year in Riga, most of them in Art Nouveau style and most of them outside the old town.