By the time I reached the trail that sagged under the bridge, the Border Patrol had been following me for at least a mile. The white-and-green SUV started tracking me as soon as I ran onto the levee and crossed in front of the old municipal golf course, where a dirt path, ridged and cracked with heavy tire tracks, led me down toward the Rio Grande. I had been running this trail for more than thirty years. Even after moving away from Brownsville for school and then work, it was here I would return whenever I came back to visit, and over time, the run had become as much of a homecoming as pulling up to my parents’ house.

Beyond the customs office on the Matamoros side, the late afternoon sun lingered behind a toxic haze of exhaust fumes, as if wondering whether it had put up with enough for one day. The two northbound lanes of the bridge, those closest to me, were choked with the cars of businessmen and their drivers returning from the maquiladoras, of dentists and doctors returning from their practices, of locals and tourists returning from the mercado, all waiting to cross into downtown Brownsville and the rest of the country, while southbound, the pedestrian lane swelled with nannies, maids, gardeners, janitors, construction workers, and high school students making their way home.

On the other side of the narrow river, a goat nibbled on a patch of dry grass and sighed, its jutting ribs distending like an accordion. A shirtless boy, as gaunt as his goat, stared over at me, an American in shorts, about to run under the bridge for no particular reason. Six foot five and light-skinned, un güero, I probably didn’t look like a Mexican to him, at least not the type the Border Patrol would be following. And yet there was the white-and-green SUV not far behind, 150 to 200 feet at the most. The dirt along the bank was soft, and I had to be careful not to twist an ankle as I stole a glance over my shoulder. It occurred to me that I should turn around and ask the agent why he was following me. It also occurred to me that no one else was on the trail and that the agent might ask me what I was doing down here and want to see some ID and that I might say I didn’t bring it because I was just going for a run and that he might say this is government property and not a running trail and that I might say this is where I ran when I was growing up and even now when I visited my family and that he might tell me it’s time for you to find a new place to run and that from that point on the conversation might not go anywhere positive. And then it occurred to me to just keep running.

Did I mention this was the summer of 2010, not long after the latest call to secure our border? A call that had started with the threat of terrorists at our back door, which later became a call about foreigners entering the country illegally, which became a call about foreigners taking jobs from Americans, which became a call about spillover violence from the drug cartels. First came the giant portable spotlights and ground sensors along the river; then the heavy machinery to clear out the brush that might hide someone taking cover; then the agents, hundreds of them, with night vision goggles and thermal imaging equipment, on bikes, on horses, in boats, near the river and the beach, around downtown and the mall, in the bus station and the airport, outside restaurants and hotels. And then came the eighteen-foot-high fence.

The Department of Homeland Security built most of the fence in rural areas, where the vast tracts of farmland made it easier for someone to cross into the country undetected, but the agency had also planned to cut through a section of the University of Texas at Brownsville, leaving 165 acres of the campus on the south side of the fence. UTB challenged the proposal until the government revised its plan, but even so, a scaled-back version of the barrier now stood between the campus baseball field and the golf course, where the agent had started following me.

Just as I was about to cross under the bridge, I glanced back again, and the SUV had disappeared. I had no idea where it had gone, where the agent could have turned around on the narrow path. A few years earlier, I had been running through here in the morning and nearly tripped over a rolled-up tarp that had a man’s bare leg sticking out of it. From the blood-caked scratches, it looked as though his calf had been snagged on barbed wire. Half the tarp lay on the path; the other half was flopped over in the deep brush, as if the bundle had fallen out of the back of a truck. As I came close, a low moan bubbled up from under the sheeting. Suddenly, the tarp snapped back and a homeless man, his face and beard smeared in streaks of what looked like motor oil, sat up, a pipe of some sort in his quivering hand.

“What’s it to you?” he yelled. “Eh, what’s it to you? Get your hands off me, you hear?” He tried to untangle himself from the tarp and stand, but by then I was already down the trail.

My father, whose work for the USDA involved patrolling the river, must have often seen worse. For 33 years, he rode on horseback along these same banks, watching for stray or smuggled livestock coming into the country. He carried a service revolver in his holster in case he ran into trouble in the brush, whether the trouble was a rattlesnake or a drug smuggler. From 1949 to 1982, he covered an area of roughly sixty miles along the sinuous course of the Rio Grande, from Santa Maria to the Gulf, including this stretch of the river close to town.

Growing up, I knew the river was where my father worked every day. I’d seen his journal, where each night at our kitchen table he noted his duties, like where he had patrolled and for how long. Here’s his entry from April 22, 1979: “HB from Willman farm to E. Lopez field and from B&M Bridge to Champion field. 7 hrs.” I didn’t know where these farms or fields were, but I knew where the bridge was. My father never talked about what he did for seven hours, and since he might say it wasn’t safe and try to stop me, I never told him that I ran along the river. For a few minutes, though, we had traveled on the same path, seen the same stooped women tending their laundry on the opposite bank, and felt the same breeze coming off the water and through the giant reeds.

A swift current of dampness eddied around me as I dipped beneath the bridge. Only faint traces remained of the drifters who slept and drank here when it was too hot above, which turned out to be most of the year. The Border Patrol must have pushed them all out—along with their shopping carts and sleeping bags and tattered clothes and jugs of wine and boxes of fried chicken and trash bags stuffed with aluminum cans that they sold to buy more jugs of wine and boxes of fried chicken.

You might think this was a weird place to run, even dangerous, and that I was asking for trouble—from the Border Patrol, from homeless guys wrapped in tarps—and you might be right, but it’s not like there are that many places to run in Brownsville. Even in the mid-seventies, when I started running, there were few choices. Back then I could climb over the eight-foot-high fence at the stadium and do laps until I got bored or the guard came around and told me to leave. Running in the streets had its own challenges. This is, after all, a border town, a place where the drivers from this side of the river complain about drivers from that side, and the drivers from that side complain about drivers from this side, and they’re both right. And if it wasn’t the bad drivers, it was the stares from people who had never seen someone run in the streets who wasn’t also being chased. So running along the river was easier, and in some ways, it was safer. At least it felt that way.

In the beginning, I ran only at the golf course. I was still in junior high, so my mother or father would drive me there, or I’d ride my bike and chain it up near the clubhouse. Sometimes there would be other runners, usually men in their thirties and forties. I was an average runner, never with much stamina or speed, but later, when I could make it the whole distance, I’d take the back way out of our neighborhood, past the projects and the free clinic and Lincoln Park and Holy Family Church, until I reached the slope up to the levee and then the golf course. From there, a path followed a horseshoe shape lined with carrizo stalks that in some areas formed a canopy high enough to run under. The huisache and mesquite, and the occasional sabal palm, acted as a natural barrier against any shanked golf balls. A hard rain could turn the trail into more of an obstacle course, forcing you to brush aside waterlogged branches as you hurdled muddy lagoons and slapped at newly hatched mosquitoes. The last half of the trail was parallel to the river, maybe three hundred feet away from the edge of the water. One afternoon I spotted a young Mexican couple crouching in the thick brush, waiting for their clothes to dry after their swim across the river. The end of the trail connected to a paved levee that ran in front of the clubhouse and led me back to the beginning of the trail. One lap came out to just about three miles. After I grew tired of the same route, I found the dirt path that took me from the levee down to the river.

When I moved away and came home to visit, I would run by the golf course but stay mainly along the river. By then things had started changing, and kept changing each time I returned. The people I knew in the neighborhood—my aunt and uncle, my cousins, family friends—either died or moved away, some of them so far that it was as if they had died. Lincoln Park disappeared when it turned into a four-lane highway that connected to a new international bridge, one built to divert the eighteen-wheelers headed in and out of Mexico. Holy Family, the church in which I had grown up, became the church where we held my father’s funeral. And then a few years after that, my mother would tell us she was ready to sell the house, and did a couple of months later, after living there for 58 years.

When I came out on the other side of the bridge, another Border Patrol agent was sitting in his SUV, waiting for me, which explained why the first one had drifted off. The trail continued along the water’s edge and, less than a mile away, came to what everyone called the “old bridge.” To get there, I would have to pass the SUV, which meant the agent would probably track me for the rest of my run. I knew what to expect by now, but I didn’t want to give him the satisfaction of knowing that I knew he was there or that I cared. I stopped and pretended to check my watch, as if I had been timing myself this whole way, oblivious to whatever surveillance they had me under. I pushed a couple more buttons on my watch and hiked up the embankment to a city park with a nice view of the river and several landmarks, including one with a plaque detailing some of the city’s shared history with Matamoros.

Inside the park, two men wearing orange-colored vests stood in front of a truck, looking at a blueprint splayed on the hood. The taller of the two men pointed off into the distance, as if he were giving directions to the old bridge that they could both already see. This would be the final stage of the border fence being built through Brownsville, skirting along downtown, near the historic district and bus station. Set on this rise, the vertical steel beams, each inches apart, would loom higher than some of the buildings in the area.

Neither man looked up when I walked by. I could have been another tourist wanting to take a look at the river, or maybe a homeless man coming up from under the bridge to get some fresh air. I might have even been someone who had just waded over to this side and was now wondering if he would ever get back to where he came from.