Art Nouveau monuments are now recognized by UNESCO on their World Heritage Sites list as significant contributions to cultural heritage. The historic center of Riga, Latvia, with "the finest collection of art nouveau buildings in Europe", was inscribed on the list in 1997 in part because of the "quality and the quantity of its Art Nouveau/Jugendstil architecture". Four Brussels town houses by Victor Horta were included in 2000 as "works of human creative genius" that are "outstanding examples of Art Nouveau architecture brilliantly illustrating the transition from the 19th to the 20th century in art, thought, and society".