Kawara, ceramic rooftiles originally introduced from Korea for early temple roofs gradually spread to palaces and other major buildings.
In the Edo period they began to be mass produced and came to be more widespread. By the twentieth century they had become the standard rooftile.
Old rooftiles abound. Piled in stacks against collapsing buildings there must be millions of them lying around. A lot of people use them in gardens, to make paths and raised beds.
Traditionally they have been recycled and used in the construction of walls.
Kawara fascinate me. They make great photos. More galleries on kawara can be found here