Graffiti is a type of deliberate human markings on property. Graffiti can take the form of art, drawings, or words, and is illegal vandalism when done without the property owner's consent. Its origin can be traced back to ancient civilizations such as the Roman Empire and Ancient Greece. Graffiti originally was the term used for inscriptions, figure drawings, etc., found on the walls of ancient sepulchers or ruins, as in the Catacombs, or at Pompeii. It has evolved to include any decorations inscribed on any surface that are considered to be vandalism or pictures or writing placed on surfaces, usually outside walls and sidewalks, without the permission of the owner. Thus, inscriptions made by the authors of a monument are not considered graffiti. The word "graffiti" expresses the plural of "graffito", although the singular form has become relatively obscure and is largely used in art history to refer to works of art made by scratching the design on a surface.