Art Nouveau architecture was popular in Riga during the late 19th century and the beginning of the 20th century – about 40% of the buildings from this time were built in this style. Several substyles formed during this period. Early elements of the new style were added to Eclectic architecture forming "Eclectic" Art Nouveau. "Decorative" Art Nouveau refers to style using only decorative elements of the Art Nouveau; the first such building was built during 1899, however by 1906 decorative styles had become unfashionable. Therefore the decorative style is not very widespread in Riga.

Most popular style in Riga is known as "Romantic" Art Nouveau – simplistic and modern in form, these buildings were decorated with elements from other historic styles and constitute about one third of all buildings in central Riga. From 1905–1911 Latvian National Romantism maximised – while being a substyle of Art Nouveau it copied forms of traditional architecture and incorporated traditional decorative elements. As Art Nouveau matured. emphasis on vertical lines became more popular, known as "Vertical" Art Nouveau, this style was most popular soon before World War I. The center of Riga is now designated as a UNESCO World Heritage site in part for its Art Nouveau architecture.

More about Art Nouveau at - http://en.wikipedia.org/wiki/Art_Nouveau