It was one of those "Eureka" moments that family-tree buffs crave. But this was not another graying genealogist scanning census records on microfilm in the windowless Minnesota History Center research library.

Robbie Black is a 12-year-old at Mahtomedi Middle School, more noted for making saves as a lacrosse goalie than preserving the past. Last year, his social studies teacher assigned him to research a Minnesota Civil War veteran named Charlie Goddard.

A sadder story would be hard to find. Goddard was 7 when his father, Abner, died in Winona. All nine of Charlie's siblings died in early childhood. When he was 11, his new stepdad drowned in the ­Mississippi River.

At 15, Goddard lied about his age and joined the fabled First Minnesota Regiment and headed to the Civil War, only to miss the Battle of Bull Run with dysentery. At Gettysburg, Goddard was wounded in the left shoulder and left thigh. He returned to Winona and managed a lumberyard before dying of tuberculosis at 23.

Back to Robbie, who shared some of his findings his with father, David Black, who is deep into family research and started noticing some ­parallels. Both Goddard and Robbie's great-great-great-grandfather, Reuben Black, were born near Lancaster, Pa. Both mustered into the Civil War army in Winona and trained at Fort Snelling. And both worked at a Winona ­lumberyard after the war.

"I started asking Robbie questions about the likelihood that these soldiers knew each other," David said.

Thanks to the Minnesota Historical Society's website — mnhs.org — Goddard's handwritten letters home to his mother have been scanned and transcribed and are easily accessible. The father-and-son detective team needed to type only three words into the search box in the upper right-hand corner of the home page: Goddard, letters and Reuben.

Of course, retracing history is never that easy. And it's the little inconsistencies that befuddle many researchers. In this case, Charlie Goddard as a teenager sometimes misspelled Reuben's name, dropping the first "e" from his curvy cursive handwriting in letters to his mother likely written by candlelight in some Civil War tent.

The Blacks overcame that hurdle. Two of Goddard's letters spell Reuben correctly and three drop the "e." In one, written when he was 16 from Camp Stone in Virginia, Goddard writes, "I heard by one of the recruits that Susan Moor[e] is married to Ruben Black. I could not say that it is so but I never would have thought of them joining in the bonds of matrimony."

In another letter, written 10 months later on New Year's Day 1863 from "Camp near Falmouth," Va., Goddard is telling his mother about the nice weather that is bound to change. He predicts, before long, they will be in "mud up to our knees."

In his very next sentence, Goddard writes: "Ruben Black and Susan Moor[e] are at last married. I hope it is a happy union, but it seems it took two reverend gentlemen to marry them."

So there it is, right on the Internet: a connection between Robbie's social studies assignment and references to the marriage of his great-great-great-grandparents.

"I felt connected to what we were learning about in social studies," Robbie said.

His father called it a "rather momentous finding" that he was tickled to share "with ­Robbie at my side."

Not that all the questions have been answered. Why was Goddard surprised that Robbie's great-great-great grandparents got married? And why did it apparently take two attempts with two reverends to exchange the vows?

That's precisely the kind of one-thing-leads-to-another mystery for which history junkies long. And as is often the case in family history research, sometimes you find unsavory things, too. (Just ask actor Ben Affleck, who tried to suppress his slave-owning ancestor from the "Finding Your Roots" show on PBS.)

In Robbie's case, his great-great-great-grandpa, Reuben, was out of work after an 1857 financial collapse when he took a job in 1859 as an overseer of black workers in Virginia. How does a former overseer wind up fighting for the North to end slavery?

The more riddles solved, the more questions asked. And Robbie said the whole experience makes him want to delve deeper into his ancestors.

To wit: Reuben's younger brother, William Black, graduated first in his class at West Point Academy in 1877 and served in the Spanish-American War, leading a team to recover bodies and salvage the forecastle of the USS Maine near Havana, Cuba. He was later in charge of sanitation at the Panama Canal construction project.

And then there's Reuben's older brother, James, who ran for president in 1872 on the Prohibition ticket, garnering 5,607 votes (1 percent) to finish fourth behind Ulysses S. Grant.

Another of the brothers, Thomas, served in the Civil War and wound up farming near Milbank, S.D., next door to Reuben. Pinpointing where Thomas is buried in Milbank and trying to procure a military headstone are among the Black family's next history projects.

Robbie makes sure to credit his late great-aunt, Doris, who compiled a detailed family history in the 1970s. "That's where a lot of my information came from," Robbie said. Without her biographies of Reuben and his brothers, he never would have been able to connect his family with the subject of his social studies project.

In other words, Robbie was part of a three-generation team that earned an A- on that assignment.

Curt Brown's tale on Minnesota's history appears each Sunday. Readers can send him ideas and suggestions at mnhistory@startribune.com.