Much has been made of the perils undocumented workers face crossing the southern border of the United States in search of work and a better life. For Central Americans, the U.S. border marks the end of one of the longest, most treacherous migrations on the planet. Still there has been a rise of 50 percent of undocumented Central Americans from Guatemala, El Salvador and Honduras living in the U.S. since 2000.

According to the World Bank (2007) in El Salvador and Guatemala the annual GNI (Gross National Income) per capita hovers around U.S.$2,500, but Hondurans' annual GNI per capita is only U.S.$1,600; all are less than one-third of the annual per capita GNI enjoyed by Mexicans. Their incentive is clear, but nothing can prepare the migrant for what lies ahead after easily crossing the porous southern border of Mexico.

Migrant jungle routes are well-known to maras criminal gangs who lay in wait to rob, beat, and murder the unlucky migrant. One week before my arrival, a Guatemalan man's body was found in the forest, where he tried to sneak around the infamous Hueyatan/Arrocera immigration checkpoint in Chiapas state. He had been decapitated. His severed left arm was never found. Viviana Alvarez, a Mexican volunteer working at the Hogar de la Misericordia shelter for migrants, told me that many female migrants who ride El Tren de la Muerta or "The Train of Death," accept the fact that they are likely to be raped.

"The Train of Death" used to start from the southern border city of Tapachula, Chiapas, but a hurricane in 2006 sent floods roaring down from mountains crowding the coast, washing out bridges. Now Central Americans must find their way 270 km (180 miles) north to Arriaga either by group van, getting out and walking around three immigration checkpoints, or if penniless, they must walk the whole way. It is in the forests and pastures behind these immigration checkpoints that the maras lay in wait for their prey. Migrants are well aware of this but in the mental calculus driven by poverty they warily accept the risk.

If they can make it as far as Arriaga, Chiapas, "The Train of Death" comes and goes every three days. When there is rain, the train is treacherously slippery. Because it is a freight train, there is no cover for the three-day journey to Mexico City. Migrants who hunker down on top are vulnerable to low-hanging tree branches, exposed to wind, rain, or the scorching sun. Some can find limited shelter in between cars underneath the ladders of grain hopper cars but the wheels of the train are then very close by and the migrants frequently slip or fall down in their sleep.

Maras hide in the jungle crowding the rails and can outrun the slow-moving train, climbing on top with clubs, machetes, knives or pistols to beat, rob and rape migrants. Most victims are simply thrown off the train, often dying from the fall. Three days before my arrival, according to Sister Lillian Bernice Long of the Shelter of Jesus the Good Shepherd in Tapachula, another Guatemalan man was thrown down from the top of a grain hopper car after being brutally beaten. Before he could stop his downward progress by gaining a grip on the steps of a ladder, the great steel train wheels severed one of his toes. He secured himself with both hands, now in tremendous pain. One of the maras descended the ladder and began stomping his foot on the victim's hands until the Guatemalan man fell under the train's wheels, severing his entire right leg. Having lost so much blood, he was not expected to survive. Somehow he did.

In the final hours before the train arrives in Mexico City, it climbs up from the lowland tropics to the 2,200 m (6,000 foot) high Valley of Mexico, plunging temperatures from the 30s C (high 80s F to the low 90s F) to 10 degrees C at night (50 degrees F) even in summer. The migrants suffer terribly from the cold especially if it has been raining in the lowlands.

North of Mexico City, migrants spread to the winds. Many take trains part of the way but eventually all must find sympathetic northbound truck drivers willing to allow them to ride in back. By the time Central Americans reach El Muro de Verguenza ("Wall of Shame"), the name attached to the U.S. border fence south of the border, deep fatigue has firmly taken hold. What for Mexican migrants marks the beginning of a hard journey marks the end for Central Americans of what has already been one of the longest, most treacherous migrations in the post-modern world, all for the chance of a better life. But there are no guarantees, because next they have to cross the U.S. border.