The Texas grave of Juan Vargas, who will be honored Sunday. (Toni Delgado)

A group of mostly strangers will gather in a soggy cemetery on Sunday, stand around the grave of a Mexico-born man they never met and celebrate a significant moment: his citizenship.

Not his U.S. citizenship.

His Republic of Texas citizenship.

If that gives you pause, that’s okay. If there is one issue that should force us to stop accepting simplistic, easy-to-debate narratives, it is immigration. The historical fluidity of our borders, despite crowd-pleasing sound bites, is not as clear cut as a line on a map and illegal versus documented.

Understanding and acknowledging that matters more than ever now because we are at a point in our history where U.S. citizens with Latino last names are being asked to prove their American-ness.

In an alarming report from my colleague Kevin Sieff about a surge in passport denials for Latinos along the border, he details the experience of a former U.S. soldier. The man, who has an American birth certificate saying he was born in Brownsville, Texas, tried to renew his passport and received a letter from the State Department saying it didn’t believe he was a citizen.

The 40-year-old was asked to provide what many of us would struggle to find: “evidence of his mother’s prenatal care, his baptismal certificate, rental agreements from when he was a baby.”

That man asked Sieff not to reveal his last name because he feared repercussions from the government — his government.

But his first name said enough. It was not Mike or Mark or John.

It was Juan.

Well, here is the story of another Juan, a man whom I have spent a lot of time learning about lately and whose place in our country’s history speaks to why it is dangerous to start judging people’s worthiness to live in this country based on their names.

Juan Vargas arrived in San Antonio with his wife and daughters when mesquite trees covered the landscape and homes were scarce. Texas was still part of Mexico then, but it would soon become its own Republic and then eventually part of the United States.

First though, there would come a fight — one that would become known as the Battle of the Alamo.

Don’t worry, this is not a history lesson. This is about what is happening at this moment.

Just a few days ago, Sen. Ted Cruz (R) referenced that battle on Twitter, commending the State Board of Education for deciding to continue describing the Texans who defended the Alamo as “heroic.” He wrote: “For generations, Texans have drawn inspiration & strength from the brave men who fought and died for independence at the Alamo. They remain a symbol of valor for all Americans.”

One of the most famous of those defenders is, of course, Davy Crockett. A Disney movie was even made in his name.

But Juan Vargas was also there.

He was a landowner when he saw the Mexican troops sweep into the city and take what they wanted — including him, according to several accounts.

“I waited on them, performed kitchen and equipage tasks about the camp,” he recalled in an interview that was published in the San Antonio Light newspaper in 1910 and reprinted in the book, “The Alamo Remembered.”

The troops who held him captive didn’t trust him with a gun, he said.

“I refused to go to the Alamo,” he said. “For this they threatened execution when the day was won but could not at that time waste a shell on me. One shell might mean victory or defeat.”

From the camp, he recalled hearing the “roar of the artillery” and the “groan of dying soldiers.” He also heard the repeated cries of “muerte a los Tejanos,” death to the Texans. He watched as Mexican soldiers returned with wounds and the dead were left in a pile in the camp, uncounted.

“Oh, señor,” he told the reporter, “that day is one to go down in history, for never did [a] patriot band go more willingly to death than those handful of Texans imprisoned behind stone wall and fighting to the last. And never in history is there recorded a battle in which so few gave death to so many.”

When the reporter interviewed him, he was already an old man and knew he was dying. The reporter described him as 114 years old. It seems an impossible number to believe, but the reporter noted that five generations of his family were alive at that time, down to a ­3-year-old great-great-grandchild.

A proclamation signed by former San Antonio Mayor Lila Cockrell also lists him living to be 114 and declares Sept. 14, 1980, to be “Juan Vargas Day.”

On Sunday, a group of his descendants will gather at his San Antonio grave for a ceremony in which the Daughters of the Republic of Texas — which is made up of the descendants of those who “rendered loyal service for Texas” before it became part of the Unites States — will grant him a medallion acknowledging him as a “citizen” of the republic.

Some of those in attendance will have not met before that moment. Many came together through a private Facebook page, where more than 300 of Juan Vargas’s descendants have found one another. I know this because my siblings and I are among them. He was our great-great-great-grandfather on my father’s side.

He is also the reason when people ask me about my family’s history — or when I hear about lifelong Texans being forced to prove they are Americans — I pause.

Immigration is about people, not just land, and so our discussions about it have to be about lineage, not just lines.

The other day I was speaking on the phone with a Washington, D.C.-area resident who was explaining why he was angry with “illegals” and at one point, he demanded to know who crossed the border in my family.

“Who was the first who walked over?” he shouted.

I tried to explain that history wasn’t that simple, that sometimes borders cross people. Sometimes you can call a place home and risk your life for it and find that even if you don’t change, that place does.

He didn’t want to hear that. He preferred the simple narrative.