Some of PBS’ biggest hits over the past three decades involve the Civil War and period dramas: Ken Burns’ nine-part documentary “The Civil War,” and British drama import “Downton Abbey,” which begins its final season on PBS in January. And on Jan. 17, PBS will launch a new series that mashes up elements of these greatest hits: “Mercy Street,” a show set in a Civil War hospital in Alexandria, Virginia.

“The truth of the matter is, the reason most of what we do in the drama space is British, economically, we’re only paying a fraction of the cost,” PBS chief programming executive Beth Hoppe told me. “We can’t do American drama all the time.”

But Hoppe wants to be able to do several, fact-based historical dramas a year. And while “Mercy Street” “actually started as a docudrama about Civil War medicine ... as it developed, it was so rich we kept going with it and said this story is so rich it has the potential to be a full-on drama and engage our audience in ways that documentary just doesn’t engage them.”

Financial constraints contributed to the shift from “Mercy Street” as a docudrama or a story about the staff of a field hospital to the show in its present form.

“We came up with a concept that was more of a ‘M*A*S*H*’ concept,” co-creator Lisa Wolfinger said of her early conversations with fellow executive producer and ‘E.R.’ veteran David Zabel. “It was based in a field hospital and it followed the Army of the Potomac around. It was certainly a Union project at this point ... I thought about the practicalities and the budget and the kind of budget that PBS would be able to put together, and I thought this was too ambitious. We would have to see every battle. We’re talking about thousands of extras and we just can’t go there.”

But tying “Mercy Street” to Alexandria opened up new dramatic and thematic possibilities for the series.

“I realized the best way to focus it was probably to focus on a general hospital,” Wolfinger told me. “For the first time you have hospitals, general hospitals. Prior to the Civil War, they were hospitals for the indigent, the poor. If you got sick you were treated in your home ... As I dug more and more, it just became more and more exciting. Here was a Confederate town, occupied by the Union all four years of the war.”

The Confederate-leaning family who had their mansion requisitioned by the Union Army to be turned into a hospital insisted on heading behind Confederate lines.

“The very last element that really clinched it,” Wolfinger said, “was (that Alexandria) start(ed) to get this mass of slaves, runaway slaves, refugees, heading north, trying to get into Union territory. And of course once they reached Union-occupied Alexandria, they didn’t have to get any further. You end up with this huge ghetto town surrounding Alexandria, and this big population of what they called contraband.”

That period setting and an opportunity to explore a moment when gender roles, medicine, and the boundary between slaves and free people were all in flux all made “Mercy Street” an example of what Hoppe sees as PBS’ niche in an increasingly crowded landscape for scripted television: drama where the action is driven by real historical detail.

Wolfinger has a background as a documentarian, and said that scrupulous attention to accuracy and the limits of that genre informed her work on “Mercy Street.”

“Your facts, your primary source material will only get you so far, and then you’re left with hope. As a dramatist, you can fill in the blanks. As a documentarian, it’s a little bit harder to justify it,” she said. “The beauty of this is there’s a lot of primary source material about the Civil War. We have photographic evidence, material to work from even though it was carefully posed and entirely subjective ... We don’t have any iconic characters. We have kisses with history. But most of our characters are obscure, so we had the freedom to draw from fact ... Where we took some liberties was bringing them all together.”

It wasn’t just medical details where “Mercy Street” is inspired to accuracy. Wolfinger describes the series as similar to “M*A*S*H*” in its dark humor, a tone inspired by the actual writing of Civil War volunteer nurses, including Louisa May Alcott. And the series’ historical advisers gave Wolfinger and her collaborators what she describes as “reams of notes” on everything from the medical cases to the vernacular the characters used when they spoke. She compared Zabel to David Milch, who created famously colorful dialogue for his Western drama “Deadwood,” in his ability to balance historical accuracy and accessibility.

“I think that’s really the trick with period drama, finding a way to make the dialogue feel real and not as though you’ve just lifted it off of the page,” she said. “As someone who’s made a lot of docudramas, I’ve certainly had to deal with that, because the standards are even higher, you have to be rigorously accurate, but at the same time you have to give your characters dialogue that doesn’t feel completely stilted.”

Hoppe says the cast of “Mercy Street,” including “How I Met Your Mother” star Josh Radnor, who plays pioneering surgeon Jedediah Foster, “The Wire” veteran Peter Gerety as a fellow doctor, and “Scott Pilgrim Versus The World” star Mary Elizabeth Winstead as nurse Mary Phinney, embraced research for their parts, including watching their way through Ken Burns’ nine-part documentary “The Civil War.” Jack Falahee, who plays Confederate spy Jack Stringfellow, even wrote love letters in character to Hannah James, who plays Stringfellow’s love interest, Emma Green, the daughter of the Confederate family whose home was seized for the hospital.

Competing in an arena that includes series like HBO’s psuedo-historical drama “Game of Thrones” and FX’s hyperviolent British period piece “The Bastard Executioner” also meant finding a distinctly PBS way to confront the bloody realities of Civil War-era medicine.

“I personally come from the world of factual and science, and I don’t see it as violent, I see it as truth,” Hoppe explained. “It was this amazing time and turning point in medicine and medical history, and I think it was important for us to portray that. We tried to be really respectful of an audience having a threshold for that and not go too far, but in the same way we were accurate with the history, we were incredibly accurate with the science and the medical procedures that we depict.”