Guastavino tile is the "Tile Arch System" patented in the United States in 1885 by Spanish architect and builder Rafael Guastavino and was a technique for constructing self-supporting arches and architectural vaults using interlocking terracotta tiles and layers of mortar to form a thin skin, with the tiles following the curve of the roof. The basement of the Minnesota Capitol building has an arched Gustavino tile ceiling.

For more information see:

Wikiepedia "Gustavino Tile" at: http://en.wikipedia.org/wiki/Guastavino_tile

Wikiepedia "Rafael Guastavino" at: http://en.wikipedia.org/wiki/Rafael_Guastavino

St. Lawrence Basilica/Rafael Guastivino at: http://www.saintlawrencebasilica.org/guastavino.html