Humans have engaged in graffiti for millennia, from ancient declarations of love to modern political and social messages. While some view graffiti as ugly or irresponsible, others see it as a defiant artistic expression that originated as a means for marginalized groups to have their voices heard. The history of graffiti as an art form can be traced back to teenagers in the 1960s and 1970s who began tagging walls and subway cars as a means of self-expression.