Getty Images photographer John Moore has spent years covering stories about immigration between Mexico and the United States—border enforcement, drug smuggling, undocumented workers, and more. Earlier this year, he traveled south to the Mexico-Guatemala border, where Central American immigrants cross the Suchiate River, beginning their long and perilous journey north through Mexico. He traveled with some of the thousands of immigrants who ride atop freight trains, known as "la bestia," or the Beast, toward the U.S. border. Riders on the Beast risk a great deal—robbery and assault by gangs who control the train tops, or the loss of life or limb in a fall. Only a fraction of the immigrants who start the journey in Central America will traverse Mexico completely unscathed—and all this before illegally entering the United States and facing the considerable U.S. border security apparatus designed to track, detain, and deport them. Moore has captured images not only of their difficult journey, but of the faces of these travelers, telling their stories through compelling portraits taken in shelters and jails along the way.