The Trump administration’s now-infamous wall on the U.S.-Mexico border has once again taken center stage in American politics. When President Donald Trump left office, only 450 miles of his 738-mile-long, $15 billion project had been completed. The Biden administration, citing the need for a more “humane policy” toward asylum seekers, has pledged to not build “another foot” of this unfinished symbol of a draconian immigration policy, and signed an executive order halting construction, effective Jan. 27. The months ahead will be a critical test of President Biden’s border agenda. The fate of the existing portion of the wall remains to be seen, and activists have pressed Biden to dismantle both the wall and the laws that made its construction possible.

Dismantling the wall is an essential first step, but it is not enough. The wall symbolizes more than just xenophobia. It also reflects a fundamental belief that the international border is fixed in place — an assumption that long preceded the wall and will linger even if it disappears. This idea is not just historically inaccurate, but also curtails the political possibilities for a more humane border policy.

At first glance the international border might appear as a solid line on a map, but that hasn’t always been the case. Of its 1,954-mile total length traversing vast swaths of desert between the Pacific Ocean and Gulf of Mexico, more than 1,000 miles of the border are defined by rivers: the Colorado and the Rio Grande. In 1848, the Treaty of Guadalupe Hidalgo ended the U.S.-Mexican War and established the modern U.S.-Mexico border as the midline of the Rio Grande. In 1854, the Gadsden Purchase modified a short, 30-mile stretch of the western border to be the midline of the Colorado River.

The Mexican and U.S. governments soon realized that when these rivers shifted across their floodplains, questions about national jurisdiction arose. For example, an exasperated U.S. agent reported that “the lower Colorado … alters its channel from time to time, cutting off a large stretch of land on one bank and depositing the soil on the other or leaving its old bed and tearing through a large piece of silty bottom land to form a channel some distance away.” The agent went on to complain that these movements made it difficult to determine which land fell on which side of the line, an important consideration in determining jurisdiction of private land ownership, public health measures and Indian conflicts. Meanwhile, most people generally moved freely across the line.

This bureaucratic confusion was relatively inconsequential until the late 19th century, when both governments, but especially the U.S. government, began to police the movement of people across the border more systematically to determine citizenship. The fluid border became seen as a more fixed political line, at least in theory. To resolve the territorial disputes that soon followed, in 1889, Mexican and American diplomats formed the International Boundary and Water Commission (IBWC). Over the subsequent 75 years, the IBWC adjudicated more than 247 instances when the shifting channels of both rivers forced the border to be redrawn — only to redraw the border when a river moved again.

Therefore, in practice, no matter how many times the IBWC adjudicated the line, the rivers remained sources of federal consternation in defining the boundaries of national territory. Because both governments struggled to control and even define the border along the Colorado and Rio Grande, people seeking to cross the border undetected made use of the rivers, even after the U.S. Border Patrol was established in 1924 to often violently police legal entry as a result of rising American racism against immigrants coming from Mexico. For the Border Patrol to enforce immigration along the border, the line needed to clearly delineate Mexicans from Americans, including Indigenous groups who did not see themselves in either category.

For native people whose ancestral homelands had been bisected by the modern border, increasing border enforcement made them migrants on their own lands. To avoid federal oversight, they sought creative strategies to cross the border using their intimate knowledge of a river’s bottomlands. On both sides of the border, brushy tracts of willow, mesquite and cottonwood offered refuge from border officials because continuous movements across the floodplain rendered the land essentially stateless.

Along the Colorado, the Cocopah and Quechan adapted their intimate ancestral ties to the river to cross the border to evade criminal prosecution and forced enrollment on Indian reservations in the United States. In 1913, for example, a U.S. Indian agent complained that some Quechans who wanted to remain autonomous from the U.S. government “live [in Arizona] just across the river from Mexico and when trouble arises on either side they cross the river.” The river thus provided a means of Indigenous resistance to increasing border constraints and federal oversight.

The completion of dams on both the Colorado and Rio Grande through the mid-20th century ultimately stabilized each river’s channel, thus allowing the border to be more easily established and enforced along these stretches. The 1936 completion of the Hoover Dam on the Colorado River, for example, meant that the border would follow the most recent line that had been adjudicated by the IBWC. Subsequent dams reduced the river along the border to a trickle. This paved the way for the Boundary Treaty of 1970 between the United States and Mexico, which in theory settled all lingering border disputes caused by rivers.

But in reality, the border still rests on shifting sands along these rivers — and is still susceptible to the environmental changes they bring. In one notable recent example, according to a report by the Texas Tribune and ProPublica, a privately funded portion of the border wall along the Rio Grande is at risk of falling into the river as fluctuating water levels erode its foundation. And people migrating into the United States from Mexico continue to cross the border along the rivers because they offer “the fastest route to American soil.” Such crossings too frequently end in tragic drownings, however. The swirling current spares neither body nor wall.

In short, borders cannot be truly fixed. Our preoccupation with the need to “control” the border neglects the fact that the landscape makes a mockery of such attempts. Instead, seeing the border as provisional and fluid might help us soften the binary distinctions between “us” and “them” that a wall tempts us to make. The wall today may be incomplete and inert, an unfinished relic from the Trump era. But its ghost still haunts the borderlands.