Natural Migration vs. Human Boundaries Theme Analysis

The title The Line Becomes a River describes the U.S.–Mexico border: a straight line drawn arbitrarily through the desert until it meets the Rio Grande on the western edge of Texas, where the line becomes a river, flowing to the Gulf of Mexico. The river itself is a site of the natural migration of fish, and elsewhere, Cantú describes other natural migratory phenomena, such as those of birds and insects. With these details, Cantú underlines the contrast between the way that humans enforce hard and arbitrary borderlines and the way that creatures move fluidly and naturally between habitats. He argues that the very arbitrariness of human borders dooms them to failure, since they attempt to deny natural and undeniable migratory patterns. In turn, this makes Border Patrol agents like Cantú ultimately powerless soldiers in a futile war.

Cantú repeatedly describes natural migratory phenomena, such as stars, which would once have been navigational tools, and the migration of animals. On a visit to the national park where she used to work, Cantú’s mother finds the dried shell of a dragonfly larva and holds it up to Cantú, telling him, “Dragonflies migrate as birds do […] beating their papery wings for days on end across rolling plains, across long mountain chains, across the open sea.” The timeless, expansive landscapes she describes serve as a reminder that migration is as old and natural as Earth itself. Later, while working as a patrol officer, Cantú sees a snake trying to cross the desert, stuck at the pedestrian fence that marks the border with Mexico. The snake repeatedly hits its head on a fence until Cantú guides it to an opening and it slithers through. The episode highlights how arbitrary human boundaries are compared to wildlife corridors—the routes animals have followed across landscapes since long before nation states were established.

Cantú also repeatedly notes that, like other nomadic creatures, humans used to cross the border easily, too, going back and forth until the escalation of border enforcement began in the 1990s. When he meets his coworker Manuel’s parents, they reminisce about the trips they used to take into Mexico. “People would cross back and forth all day long, like the border wasn’t even there,” Manuel’s father explains. Cantú uses this contrast between the recent past and the present day to argue that the current violence and policing on the border, though taken for granted today, are not natural or intrinsic to the region. Cantú’s own family history also highlights the ways boundaries rupture natural migrations. When Cantú’s mother falls and hurts her ankle on a trip to Ciudad Juárez (just before Cantú starts work as a patrol officer), a Mexican man helps take care of Cantú’s mother and tells them, “You’re at home here.” And yet, though Cantú and his mother’s family traveled from Mexico to the United States just a few generations earlier, the countries are so divided physically and politically that they’re not at home at all.

Cantú also describes the arduous, entirely arbitrary, and highly politicized process of determining and marking the present-day border between the U.S. and Mexico, thus questioning the validity of the very boundary he is paid to enforce. By highlighting how arduous the process of marking the border is for the first surveyors, he underscores exactly how unnatural it is to score a boundary into such a region. “The surveyors,” he writes, “could not help but comment on the strangeness of their task and the extreme and unfamiliar nature of the landscape.” They also remarked upon the “’arbitrarily chosen’ nature of the boundary line and the ‘impracticable nature of their work’”—precisely the improbable work that Cantú and so many others are paid to enforce, inflicting great and widespread misery in the process. By describing mapping the border onto the landscape as the assertion of “a boundary that had hitherto existed only on paper and in the furious minds of politicians,” Cantú highlights that this enormous, misery-inducing obstacle was created in part out of the personal emotions of just a few men. Further, he suggests that all future attempts to uphold this boundary asserted out of fury will similarly be marked by suffering and fury. In this way, he reminds readers that the border has enshrined ongoing suffering for purely arbitrary reasons and will never be defensible as a purely rational phenomenon.