AMNA NAWAZ: As Russia prepares to launch a new large-scale spring offensive, one city just 15 or so miles from the front line is preparing for the worst.

Control of Izyum is vital for Ukraine, strategically linking the Kharkiv region to Donetsk.

Izyum was occupied by Russian forces for six months in the spring of 2022.

Ukrainian forces liberated it and exposed brutal Russian war crimes.

Now that threat of occupation is again all too real.

Producer Amanda Bailly in Izyum and Nick Schifrin report.

NICK SCHIFRIN: In Eastern Ukraine, a frontline city once again braces for battle.

Izyum's streets and buildings are covered with hundreds of miles of nets to try to protect from Russian drones, as the city's scars remain unhealed.

Everywhere here, there are painful reminders of Russian bombardment and a brutal six-month occupation in 2022.

Perhaps more than any other city, Izyum today combines Ukraine's pain from its past with fear for its future.

Russian troops and the front line are only about 15 miles away, and Russian missiles strike next to residents' homes.

Serhii Saltovskyi has lived here all his life.

These days, he fears he may have to take his family and leave.

SERHII SALTOVSKYI, Resident of Izyum, Ukraine (through translator): We are always talking about the front getting closer.

It's difficult to imagine testing your destiny again.

I don't know how you could overcome it twice.

NICK SCHIFRIN: This former school is the scene of his suffering.

During the occupation, Russian soldiers took over the building and one day brought him inside.

SERHII SALTOVSKYI (through translator): I was tortured with electricity in the basement.

I was in there for almost 24 hours.

They beat us up.

They took us to the forest and pretended to execute us.

They did whatever they wanted with us.

The streets were full of dead bodies.

We were not human beings for them.

We were slaves.

NICK SCHIFRIN: One resident was enslaved in this shed, Alah (ph), who counted the days of her detention by scratching them on the wall as Russian troops tortured and raped her.

Others were slaughtered.

In September 2022, Izyum was liberated and revealed the death of Russia's dehumanization, more than 1,000 people killed, more than 400 buried in a mass grave.

For many victims, there were no names, no markers of lives lived, only numbers.

And Russian occupiers forced Saltovskyi to bury his neighbors' bodies.

SERHII SALTOVSKYI (through translator): I try to forget, but it's very difficult because it's stuck in the soul.

From time to time, the memories and images just appear.

If you haven't lived through occupation, it's impossible to understand what we lived through.

NICK SCHIFRIN: Today, the crosses mark no bodies.

They're instead standing reminders of Russian war crimes.

It is a living memorial and a hope that Ukraine can ensure, never again.

The bodies have now been reburied properly, although some are still unidentified.

OLEKSANDR KOBOLEV, National Police of Kharkiv Region (through translator): You understand that behind every grave is a human life.

The overwhelming number of these dead are civilians.

NICK SCHIFRIN: Oleksandr Kobolev is the region's lead war crimes investigator and was one of the first on the scene in 2022.

OLEKSANDR KOBOLEV (through translator): It was terrible, to be honest.

It's hard to describe in words.

There were also people who were executed.

Some were kept in torture chambers.

A lot of these people are people who died as a result of an airstrike on a five-story building.

NICK SCHIFRIN: Killed in that strike, entire families, including 6-year-old Olesya Stolpakova (ph), her older sister, 8-year-old Sasha, both their parents and maternal grandparents, their bodies buried in the mass grave, their likeness drawn on the building where they died.

Across the city during occupation, residents labeled their doors with the words "Kids," "People," a desperate plea for humanity that the invaders denied.

Today, in Ukraine, there is a collective trauma that does not spare its children even during this holiday to welcome spring.

YULIA NYSOVA, Displaced Ukrainian (through translator): The explosions are getting louder and louder, and the front line is getting closer and closer, so I don't know what is next for us.

NICK SCHIFRIN: Yulia Nysova moved to Izyum after being displaced three times.

She's worried that the war will force her and her family to flee yet again.

And yet her daughters try their best to celebrate this holiday, which marks new beginnings.

NICK SCHIFRIN: And Nysova knows that kids need space to be kids and enjoy Slavic traditions together.

YULIA NYSOVA (through translator): They have been doing online school for four years now, so it's important for them to still socialize and communicate.

NICK SCHIFRIN: For Izyum's residents, the daily drumbeat of life is a kind of defiance to the doom of the front line just outside the city's walls.

Izyum is known as the City of Heroes for what it survived, and communal support is an antidote to trauma.

The facade of Izyum's women's center is still crumbling from a 2022 Russian strike.

But, inside, psychologist Natalia Noshenko (ph) runs art therapy classes to help heal invisible injuries.

Tetiana Shapovalova stayed in Izyum through occupation with her then-6-year-old son.

Their wounds are still deep.

TETIANA SHAPOVALOVA, Resident of Izyum, Ukraine (through translator): My son is a very strong person.

We went through hell, and he's so brave.

I'm always checking in and asking, how are you?

NICK SCHIFRIN: Today, she and her son have decided never again to risk those horrors, and so they will leave if the threat comes too close to home.

TETIANA SHAPOVALOVA (through translator): I don't want to stay here if there's real danger, because it's my child's life and my responsibility.

Half of my stuff is already in boxes.

NICK SCHIFRIN: Fifty-six-year-old Larysa Yerokhina has lived here for two years.

Her village Bohuslavka was first occupied in 2022, with Russian troops destroying much of the settlement.

Ukrainian soldiers liberated it, but now it's under siege again.

LARYSA YEROKHINA, Displaced Ukrainian (through translator): Our whole street is destroyed.

My home doesn't exist anymore.

NICK SCHIFRIN: She shows photos of her home the day she evacuated and what it looks like today, reduced to rubble by a Russian strike.

LARYSA YEROKHINA (through translator): There was a kitchen there and this was the house.

NICK SCHIFRIN: Grief for a home and life shattered by war is heavy.

And so now she needs to create a new home.

The drawing says "Izyum, a safe space," an adopted home that provides her support.

LARYSA YEROKHINA (through translator): We are strong.

Everything is going to be OK.

We will overcome it.

Everything is going to be OK.

NICK SCHIFRIN: Resilience, yes, but, here, even soldiers appeal to the divine for protection in this once captured city facing an uncertain future.

For the "PBS News Hour," with Amanda Bailly in Izyum, I'm Nick Schifrin.