A few days later in detention, Maria pulled up her sleeve and Peter saw the bruises. They didn’t say a word, just nodded at each other. In that moment, they both understood: the secrets no longer had to stay hidden. It was time to ask for help.

Modern graffiti began in big cities in the United States in the 1970s. In New York, young people wrote their names, or 'tags', in pen on walls around the city.

One of the first 'taggers' was a teenager called Demetrius. His tag was TAKI 183. He wrote his tag on walls and in stations in New York. Other teenagers saw Demetrius's tag and started writing their tags too. Soon, there were tags on walls, buses and trains all over New York.

Then, some teenagers started writing their tags with aerosol paint. Their tags were bigger and more colourful. Aerosol paint graffiti became very popular in the 1970s and 1980s. It appeared on trains, buses and walls around the world.

In the 1990s and 2000s, a lot of graffiti artists started painting pictures. Some artists' pictures were about politics. Other artists wanted to make cities beautiful and painted big, colourful pictures on city walls.

Graffiti in galleries

In some countries, writing or painting on walls is a crime. Sometimes, graffiti artists have problems with the police. In other countries, artists can draw and paint in certain places. For example, in Taiwan, there are 'graffiti zones' where artists can paint on walls. In São Paulo in Brazil, street artists can paint pictures on walls and houses. Their pictures are colourful and beautiful. Some tourists visit São Paulo just to see the street art!

In Bristol in the UK, there is a street art festival in August every year. Artists paint all the buildings in a street. Lots of people come to watch the artists and take photos. You can see exhibitions of street art in some galleries too. There have been exhibitions of street art in galleries in Paris, London and Los Angeles.

Who are the artists?

Some street artists have become famous. Here are three stars of the street art world:

• Os Gêmeos are twin brothers from São Paulo. They paint big, colourful pictures of people on buildings. In 2007, they painted a castle in Scotland!

• Blek le Rat is from Paris. He is famous for painting pictures of homeless people in big cities.

• Faith47 is from Cape Town in South Africa. She paints big, colourful pictures of people and animals. She likes painting in different places and you can find her work on pavements, postboxes, buses and, of course, on walls!

The future of street art

Many street artists use the internet to look at photos of street art from around the world. They communicate with other artists online and share ideas. Some street artists are famous and you can see their pictures in galleries. We don't know about the future of street art, but it is here to stay for sure!