Folk Museum which was opened in 1952 at the Glaumbær Farm. By the 20th century the design was evolving still, seeing such additions as the framhús, a kind of timber porch at the front entrance of buildings. Today grasshouses are no longer constructed in Iceland (construction stopped in the mid-20th century), and the few remaining examples are generally open to public as open-air museums. There is some evidence to suggest a Celtic influence in early Icelandic architecture in the form of stone roundhouses and sheepcotes, however much of this is still shaded in obscurity. Church buildings With the arrival of Christianity in Iceland in 1000 AD, construction began on numerous impressive churches. A majority were probably constructed out of turf, but there were also numerous timber-framed churches, however not much remains of these buildings today. The first stone churches appeared in around in the 18th century, quite late considering the significant lack of timber on the island (even access to driftwood was not widespread). Stone buildings Many high-quality stone buildings were erected in the 18th century, the first being a mansion on Viðey, made completely out of Icelandic stone. These were some of the first buildings in Iceland to be constructed by architects, who were from Denmark, as these buildings were constructed for the Danish authorities. The craftsmen involved in the construction of these buildings were also foreign. Icelandic stone buildings from this period were inherently similar to those in Denmark, save the use of timber to clad the roofs instead of slate. This type of building was considered very expensive and is seen in many official buildings such as Bessastaðir (the presidential residence) and Alþingishúsið in Reykjavík. Many Icelanders learned the craft of masonry during the stone construction boom period, leading to the building of many stone houses which mimicked the design of Icelandic turf houses. Urbanization Urbanization began to appear around the 18th century, when Danish merchants set up permanent trading posts for themselves. The timber for constructing these residential and commercial premises was mostly prefabricated and imported. These timber-framed buildings had high pitched roofs and low walls, and they were tarred on the outside making them dark in appearance. With the movement towards independence from Denmark and the implementation of Icelandic free trade, more diverse architectural styles and influences were brought to the island. Classical influences can be seen in timber buildings from the 19th century, these