The Spanish Civil War is the one modern conflict that never seems to run out of lessons to pass on to us. The intimate, epic-length Spanish drama “The Endless Trench” is one of the best illustrations yet of what being on the losing side in a fight against fascism can be like.

It’s a fictional film based on something that really happened in Spain in the 1930s. As the German, Italian, Catholic Church and Texaco-backed Falangists of Francisco Franco gained the upper hand, death squads traveled far and wide, executing Republicans or people with any suspicion of having harbored leftist views.

Many fled the country. But that wasn’t the only way of surviving this slaughter, and the decades of fascist rule that followed.

Higinio (Antonio de la Torre) hears the trucks roll into his small town. His new bride Rosa (Belén Cuesta) is awakened by the thunder of jackboots, the pounding on doors. But panicked or not, all isn’t lost. Higinio dug out a little hiding place, and that’s where he lays low as troops rush in, toss the joint and threaten Rosa, ignoring her pleas (in Spanish with English subtitles, or dubbed) that “He never hurt anyone. He shouldn’t be on a list!”

When the troops storm into the next house, Higinio attempts an escape. A neighbor (Vicente Vergara) rats him out, they struggle, and the bullets fly as our victim flees into the night.

He dives into an abandoned well, where others “on their list” hide, leading to an “I could see ALL this coming…Bullets don’t solve anything” political debate, standing knee-deep in water as Civil Guards storm by, shooting others on the run.

The wounded Higinio can’t get away, which might ensure his and the under-scrutiny Rosa’s safety. It’s back to his hidey hole. For years, as it turns out.

Three directors and two screenwriters contrive an epic story of survival, paranoia, bravery and cowardice. “The Endless Trench,” which takes its title from a surreptitiously dug escape route Higinio starts on, changes locations and with that, changes the dynamics of their relationship.

Rosa feeds him, hides him and wants something like a life, which their circumstances seem to preclude. He is forever erring on the side of paranoid caution. That neighbor, Gonzalo, really has it in for him. And we hear just enough of Gonzalo’s story to understand why that is, right or wrong.

An endurance contest begins, World War II starts and as the Allies plunge into their global war against fascism, that becomes Higinio’s hope. –“Wait for the Allied victory.” Surely they’ll come for that murderous rat Franco, afterwards.

But as years pass, and more years after that, the story that started so harrowing grapples with paranoia that grows, rather than subsiding, and something like despairing resignation sets in. It can be heartbreaking.

De la Torre, of “Marshland” and the Uruguayan political terror thriller “Twelve Year Night,” gives us a “hero” who never seems heroic. His cagey turn makes us wonder about Higinio’s “innocence” in a neighbor-against-neighbor bloodletting, and we question his manhood as he sees what his wife, who loves him as passionately as he loves her, must endure. But we never fret over Higinio’s cunning.

Cuesta (“Holy Camp!,” “Party Town”) has the more robust role. We don’t just see the physical evidence of what Rosa must endure, Cuesta makes us feel it. She married a man in troubled times, and life pretty much just stops. She stoically keeps them going, working as a seamstress. But she wants a baby. She wants to see the sea. Cuesta lets us see the resignation that Rosa is the first to embrace.

Being conditioned by Hollywood, I kept waiting for something distinctly Spanish — probably involving a knife — to transpire between Higinio and his Javert, the relentless Gonzalo, given a dogged self-righteousness by Vergara.

Some of the episodes that put Higinio on high alert and make us fear for him come from expected quarters. Others are straight-up melodrama. But the evolving interpersonal conflicts keep “The Endless Trench” on the move.

We don’t know what’s coming, don’t know how much Higinio is responsible for his fate and can only guess if his story arc will give him, his enemies or us any satisfaction, when all is said and done.

Don’t be daunted by the running time, here. This is an intimate epic that alarms as it sprints out of the gate, settles into a lingering tension and even as it is winding down, manages to keep the viewer frightened and on tenterhooks. That’s what living under a fascist regime is like.

Rating: TV-MA, graphic violence, sex, nudity

Cast: Antonio de la Torre, Belén Cuesta and Vicente Vergara

Credits: Directed by Aitor Arregi, Jon Garaño and Jose Mari Goenaga, scripted by Luiso Berdejo and Jose Mari Goenaga A Netflix release.

Running time: 2:27