Hundreds of migrants make their way north towards the United States from Chiapas state in southern Mexico, near the border with Guatemala. Many thousands of migrants fleeing violence and poverty cross Mexico every year heading for the US border. They often travel in large groups -- or caravans -- in protest, and to protect themselves against robbery, kidnapping and extortion by criminal groups. "We go in big groups to look after one another," says one Venezuelan. IMAGES AND SOUNDBITES