If you know what younow is comment your username (:

Maybe because it was so unique, a form of art, and they could easily store things in it and no one had ever done that before. i’m not sure but that’s what i think : )

Answeryou're sixteen

The technique was mural painting and he used either freshly laid or wet lined plaster. he also use water to merge it with the pigment and plaster creating a internal part of the wall