Monk and Nun

Monk and Nun is a style of roof similar to imbrex and tegula, but instead of using a flat tile (tegula) and an arched tile (imbrex), two arched imbrex tiles are used.
The top linking tiles are the "monk" tiles and the lower layer are the "nun" tiles. Mortar is often used under the "monk" tile to firmly attach it to the "nun" tile as well as providing an extra seal against entry of rain, but it is sometimes omitted. The origin of the name is unknown, but is also known as "Priependach".
This style of roof was, along with imbrex and tegula, developed in ancient times, and is popular around the Mediterranean, France, and, during the Middle Ages it was also popular in Germanic Europe, but was later replaced by Biberschwanz ("beaver tail") roofing, although is still occasionally used, particularly for old and sacred buildings (which would have originally had Monk and Nun roofs).
In modern times this style is popular in the American southwest where it is called "Pan and Cover" or "Mission Style". An easier-to-install variant called "S-Tile" is essentially the synthesis of a pan tile and a cover tile.