forms the compact northern frontier of Stockholm's historical city centre. As described above, Lindhagen's original intentions for the elevated area was to keep it as a park featuring the 17th century avenue of Karlberg Palace. In the city plan of 1879, however, the area was divided into two large blocks, which on a request from the local landowner, porcelain factory Rörstrand, in 1886 were split up into smaller properties. This resulted in a new city plan which was adopted to local topographic variations and therefore features non-perpendicular street crossings. Few buildings were constructed before the start of the 20th century, but construction work soon boomed to culminate in 1905–06, speculation causing many buildings to change owners several times before their completion. Virtually all the buildings in Birkastaden are Art Nouveau, a result of both the brief construction period and the fact that some 50 buildings were designed by architects Dorph & Höög, at the time the largest architectural practice in Northern Europe. The buildings of Birkastan features oriel windows, towers on the corners, rounded pediments and bright, plain plaster façades with thrifty decorations. As a result of speculation, the backyards are narrow, and many flats shadowy. From the start, however, Birkastan was a mixed area shared by both low and high income earners. Röda bergen Röda bergen ("Red Mountains"), the hilly area just north of Birkastan, was unsuitable for the regular and perpendicular street pattern envisaged for Vasastaden, but proved excellent for the new city planning ideals where the terrain was allowed to govern city plans. The plan for Röda Bergen was designed by P O Hallman, who during the 1910s also produced similar plans for Lärkstaden inspired by the ideas of Austrian architect Camillo Sitte. His plan for Röda Bergen was adopted in 1909, but because of World War I most of these plans remained unrealised until the 1920s. In 1923 the plan, slightly modified by Sigurd Lewerentz, was finally established. The buildings facing the surrounding blocks are traditional 5–6 floors residential buildings forming a wall around Röda Bergen. From the monumental eastern entrance, an avenue (Rödabergsgatan) leads west to a round elevated space where a church was originally planned. Perpendicular to this avenue, the heavily trafficked Torsgatan cuts through the area. The blocks within Röda Bergen are limited to 2–3 floors and most of the backyards are open in one end, which allows for plenty of sun light