Bhutanese architecture consists of Dzong and everyday varieties. Dzongs in Bhutan were built as fortresses and have served as religious and administrative centers since the 17th century. Secular lordly houses emerged as a distinct style in the late 19th century, during a period of relative peace in Bhutan. Throughout its history, Bhutan has mainly followed the Tibetan tradition of Buddhist architecture. Traditional architecture The Driglam Namzha codifies the traditional rules for the construction of the dzongs as well as ordinary buildings. Under the direction of an inspired lama the fortress is constructed by citizens who historically participated as part of their tax obligation to the state. Modernly, however, traditional structures are built by wage laborers, straining the government's ability to repair and preserve dzongs in particular. Traditional architecture remains alive in Bhutan. As recently as 1998, by royal decree, all buildings must be constructed with multi-coloured wood frontages, small arched windows, and sloping roofs. Traditional western Bhutanese structures are often made from wooden frames earthen material, namely wattle and daub interior walls, rammed earth exterior walls, and stone and earth retaining walls. No plans are drawn up, nor are nails or iron bars allowed in the construction. Many traditional structures feature swastikas and phallic paintings. Lordly mansions of western Bhutan (Bumthang, Paro, and Trongsa Provinces) appeared in the late 19th century during a period of relative calm. Like dzongs, they are multi-storied courtyard buildings, though homes have more windows, resembling somewhat chalets. Upper floors of residences usually served as chapels (choesum) that housed paintings, statues, and religious literature. The architecture of ordinary houses varies according to location and elevation. In the southern lower altitudes, thatched bamboo houses are common; buildings progress to simple stone structures in higher altitudes. Two-storied buildings resembling but smaller than the lordly mansions are common throughout western Bhutan. Like mansions, upper floors are often reserved for chapels, which double as guest quarters. Attics, insulated with bamboo mats and hay, often serve for drying animal skins and chilies. As with most buildings, walls of ordinary homes in the west are most frequently rammed earthen walls, pounded into wooden frames for up to a week and rendered with lime. Completed mud walls may be left naturally colored or whitewashed. The wetter eastern valleys of Bhutan tend to be steep, narrow ravines, with settlements dug directly into mountainsides. Walls are more often made of stone in these regions, as