In a now-neglected book entitled Notes on the Synthesis of Form (1964), Christopher Alexander approached design as a question of “goodness of fit” between form and context. I thought about this formulation frequently when I began traveling in 2002 the entire length of the US-Mexico border on both sides, a journey of 4,000 miles. I had the good (or bad) fortune to embark before the US undertook the fortification of the international boundary line and so witnessed the border’s closure, an experience that altered my understanding of both countries.

The US-Mexico borderlands are among the most misunderstood places on earth. The communities along the line are distant from their respective national capitals. They are staunchly independent and composed of many cultures with hybrid loyalties. Nowadays, border states are fast-growing places of teeming contradiction, extremes of wealth and poverty, and vibrant political and cultural change. They are also places of enormous tensions associated with undocumented immigration and drug wars.

Mutual interdependence has been the hallmark of cross-border lives since prehistoric times. After the Spanish conquest, a series of binational “twin cities” sprang up along the line, eventually creating communities of sufficient distinction as to warrant the title of a “third nation,” slotted snugly in the space between the US and Mexico. I came to understand the third nation not as a zone of separation but instead as a connecting membrane. This way of seeing substitutes continuity and coexistence for sovereignty and difference, running counter to conventional wisdom that the border is the place of last resistance against immigrant and terrorist.

In 1848 the Treaty of Guadalupe Hidalgo established the international boundary, which was frequently marked by no more than a pile of stones. A second survey in 1892 added over 200 more boundary monuments. But in the 1990s, responding to increased waves of undocumented crossings from Mexico, large fences sprouted in border cities such as Tijuana and Ciudad Juárez. Following 9/11, the US unilaterally adopted an aggressive program of fortifying the entire line. The new barriers are without historical precedent, and threaten to suffocate the arteries of communication that supply the third nation’s oxygen.

On the US side, the border was transformed into an archipelago of law enforcement agencies dedicated to the apprehension and deportation of undocumented migrants, and supported by private manufacturing, detention and security corporations. On the Mexican side, the federal government’s war against drug cartels resulted in tens of thousands of deaths and may even have consolidated cartel power.

In places, the new Wall is sinuously beautiful as it snakes through desert, but it can hardly be construed as a good fit! Yet the environmental design responses it has provoked are immensely intriguing in their diversity. The Wall provides a canvas for artworks, or becomes an instrument to be played by musicians; and ‘windows’ cut into the Wall reduce cross-border incidents of rock-throwing. Design professionals are directly engaged in building the rising number of official Ports of Entry that establish new portals in the Wall that shuts out Mexico. My CED colleague Ron Rael has designed water, energy and anti-pollution schemes along the Wall’s length. And people invent surprising ways of going over, under, through and around the Wall.

Ultimately, the Wall separating Mexico and the US will come down. Walls always do. The Wall won’t work because the third nation has strong connective tissue that cannot be undone. The third nation is the place where binational lives and values are being created – organically, readily, and without artifice. It is the place of being and becoming between our two nations.

What should be done about the Wall that so rudely interrupts the third nation? The Berlin Wall was torn down virtually overnight, its fragments sold as souvenirs of a calamitous Cold War; and the Great Wall of China was transformed into a global tourist attraction. Left untended, the US-Mexico Wall would collapse under the combined assault of avid recyclers, souvenir hunters, and people offended by its mere existence. Nevertheless, we should preserve sections of the Wall to commemorate that fraught moment in history when the US lost its moral compass.