Every year more than a million men and women from countries like El Salvador, Honduras and Nicaragua attempt to cross the river that forms a border between Guatemala and Mexico. Their immediate aim is to enter Mexico illegally, but they have another destination in mind - the US.
Once in Mexico, they must cross the entire Mexican coast in order to reach the border with Texas. It is a journey of about 4,000km and one that begins at the Arriaga train station. The freight trains are the only means of transport for these migrants. Thousands take them every day - each trying to find his or her own spot on the roofs or the axles between the coaches.
But it is a dangerous journey towards what some call "the impossible dream" and only 40 per cent of all those who attempt it make it to the US border.
With no way of knowing where the trains are heading, some make the mistake of climbing aboard trains heading in the wrong direction - towards the Guatemalan border. Others are caught by police who regularly stop the trains in the middle of the countryside and round up all those hitching a ride. But for some, the dangers prove far greater.
One Mexican shopkeeper explains: "I've seen lots of accidents ... people who fall off the train and die because the train runs them over. People who get their legs cut off too."
Rosana is from El Salvador. She had to have both of her legs amputated after she fell off one of the trains. "I fell off the train," she explains. "I was travelling sitting on the roof. I fell off when I tried to climb down before a migrant checkpoint. As I was getting down, I slipped."
Stories like Rosana's are told across Latin America and weigh heavily on the minds of those contemplating the journey.
Thirty-year-old Jaime is from El Salvador. He first crossed the US border illegally as a child with his parents. They settled in Los Angeles where they lived for 15 years. Jaime even got a Green Card. But when he became a gang member and fell foul of the law, he was deported back to El Salvador. There he met 19-year-old Lupita, who he says transformed him.
Together they are now attempting to reach the US, in the hope of finding a better life together.
"My objective is to reach Brownsville in Texas," Jaime says. "And once I get there, to work hard to give Lupita a better life."
But Jaime says the stories they heard in El Salvador about the dangers of the journey trouble Lupita.
"They traumatised Lupita before we left, because people talk so much about these tragic accidents that happen on the journey," he explains. "Lupita often feels really bad but we're going to make it. I've never stopped believing since we set out and I'll never stop believing."
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