When I was 11, my parents moved from suburban Maryland to Germany. I spoke no German at the time. My best options were to sink or swim in a German school or to attend one run by the British Army. The latter option seemed easiest, and I wound up at Cornwall School in Dortmund—a school for the sons and daughters of British military families.

I was the only American there. I was the only kid whose parents weren’t in the military. I stuck out like the proverbial sore thumb. On my first day at Cornwall, my English teacher picked up the exercise book in which I was writing and whacked both of my ears with it. “You’re in a British school now, Santer. We write in pen and ink, not in pencil.” Welcome to the real world!

My first year at Cornwall School was character-building. I did not have the luxury of retreating into a shell, or of walling myself off from the rest of the world. Surviving and thriving required learning—and learning fast—about my new environment. Figuring out how to play soccer, rugby and cricket. Making sense of Chaucer and Shakespeare. Wrapping my 11-year old brain around the idea that the history I learned in growing up in Maryland looked a little different from a British perspective.

As the only American at Cornwall, I was a representative of my country. My fellow students, and sometimes even my teachers, asked me to justify why my country was at war in Vietnam, and why Robert Kennedy and Martin Luther King had been assassinated. I was asked, “How can you live in such a country?” I had to figure out how to respond.

I came away from my eight years at Cornwall School with an undying love of the English language, a better sense of how others viewed America and Americans, a passion for soccer, and a weird hybrid accent.

After Cornwall School I went to college in England. While working on a PhD at the University of East Anglia, I was invited to attend a climate science conference in Germany. The conference was held in a little town close to the East German border. During a lunch break, I took a walk in the woods and caught my first glimpse of the heavily fortified border between West and East Germany. I remember the razor wire, the guard towers; the village on the East German side of the wall, with smoke rising from chimneys.

It seemed so absurd and incomprehensible—to walk through a beautiful forest and then suddenly be confronted with a grim, enormous structure. A structure dividing a nation; separating families, friends and lives. I struggled to wrap my 28-year old brain around the realization that for those on the other side of the razor wire, this border was where their known world ended. It was their Ultima Thule.

Years later, I saw the Berlin Wall. After finishing my PhD in England in 1987, I was offered a position as a postdoc at the Max Planck Institute for Meteorology in Hamburg. Soon after arriving in Hamburg, I started working with Klaus Hasselmann, one of the three directors of the Institute, on the problem of detecting a human-caused fingerprint in observed climate records. My work took me to Berlin on several occasions, and “the Wall” became more than just a story in the newspaper, an object in a photograph, an imagined thing. I witnessed its reality.

November 1989, marked the beginning of the end of the Berlin Wall and the fortified border. Most of it is gone now, but bits and pieces of the Wall still remain today, an enduring monument to human folly. You can do typical tourist stuff: buy chunks of the Wall on eBay; take selfies in front of the graffiti on surviving Wall sections. Or you can probe deeper; you can try to understand the long-term consequences the Wall caused and still causes in German society. Not all Wall scars are physical.

Today, we are told, Americans need a wall on our southern border. We are told that we need the wall to keep us safe from rapists and terrorists; from those who are not like us, who speak differently, or do not look like we do.

Back in Cornwall School in 1966, I was “the other.” I was different in my nationality, in my speech and in my religion. For that younger me, safety and security did not come from building metaphorical walls between myself and my peers. Security came from listening, from learning, from seeking understanding of a world that was new to me.

Those lessons seem relevant today.

True security for our country does not come from building a wall on our southern border, or from asking Canada to pay for a wall on our northern border, or from withdrawing into our own little national cocoon. National security in a complex and rapidly changing world is best guaranteed by strong alliances, shared humanity and an accurate understanding of how and why political, economic and environmental changes are occurring. Keeping our country safe from harm requires awareness of the reality and seriousness of human effects on global climate. It requires a willingness to work with the rest of the world in finding innovative clean-energy solutions to the existential threat of human-caused climate change. No physical wall can fully protect us from that threat.

On January 1, the New Horizons spacecraft took photographs of Ultima Thule, a planetesimal 4 billion miles away from our Sun. It was an incredible triumph of science, engineering and imagination. As the borders of our known universe are expanding, strange and beautiful new wonders are revealed. Many more await. Let’s explore such borders of human ingenuity and imagination; we do not need to build another monument to human folly on our own border.