The lost art of timbrel vaulting

In its "Lost Knowledge" column, Make: Online presents an article on the lost medieval art of timbrel vaulting, an architectural technique using a "system of interlocking terracotta tiles which create what are known as Guastavino domes, after their inventor, Rafael Guastavino." (photos and diagrams)

According to the article, the construction of the vaulted domes "does not rely on gravity but on the adhesion of several layers of overlapping tiles which are woven together with fast-setting mortar. If just one layer of thin tiles was used, the structure would collapse, but adding two or three layers makes the resulting laminated shell almost as strong as reinforced concrete."