Form of visual communication, usually illegal, involving the unauthorized marking of public space by an individual or group. Technically the term applies to designs scratched through a layer of paint or plaster, but its meaning has been extended to other markings. Graffiti is widely considered a form of antisocial behaviour performed in order to gain attention or simply for thrills. But it also can be understood as an expressive art form. Derived from the Italian word graffio ("scratch"), graffiti ("incised inscriptions," plural but often used as singular) has a long history. It has been found in ancient Roman ruins, in the remains of the Mayan city of Tikal in Central America, on rocks in Spain dating to the 16th century, and in medieval English churches. During the 20th century, graffiti in the U.S. and Europe was closely associated with gangs. Graffiti was particularly prominent in major urban centres throughout the world; common targets were subways, billboards, and walls. In the 1990s there emerged a new form of graffiti, known as "tagging," which entailed the repeated use of a single symbol or series of symbols to mark territory.