On a proud June morning in 2014, Ukrainian forces restored their flag over Mariupol's city hall to rousing choruses of the national anthem. For weeks, they had engaged pro-Russian separatists in a fight for control of a port city with immense strategic importance. The loss of Mariupol, an industrial center on the Sea of Azov, risked losing control of a swath of eastern and southern Ukraine — a prize that Russian President Vladimir Putin desperately sought.

Now, after nearly a decade on the front lines of what had been a low-grade war, Mariupol's de facto fall to Russian forces stands as a landmark moment in Moscow's full-scale invasion. In a war marked by Russia's underperformance, by its inability to take Kyiv and its failed attempt to decapitate the Ukrainian leadership, control of the devastated metropolis amounts to a significant and horrific Kremlin victory.

The fight is not over. Civilians and Ukrainian fighters — including combatants from the Azov Regiment, the same nationalist unit that helped wrest back the city in 2014 — remain hunkered down in a dramatic last stand at the sprawling Azovstal Iron and Steel Works.

Outside the Soviet-era factory's labyrinthine halls and underground tunnels and chambers, there is little left to defend.

The battle of Mariupol has been an anachronistic siege — a Guernica tableau of fireballs from Russian missiles in night skies, apartment buildings reduced to smoldering husks, the destruction of museums and hospitals. Civilians died simply for the accident of where they lived, including those sheltering in a bombed theater with the word "children" painted across its front courtyard in a failed attempt to warn off Russian fighter jets.

The near-total leveling of a city has evoked the sieges of Aleppo in the 2010s and Grozny in the 1990s — but also the destruction of European cities from an age thought buried in the ashes of World War II, and, further back, the 13th-century pillaging by the Golden Horde that overran the lands where modern Mariupol now lies in ruins.

Capturing Mariupol brings Moscow a major step closer toward achieving a goal: Establishing a land bridge from the Crimean Peninsula — annexed by Moscow eight years ago — to Ukraine's breakaway republics in the east, which are effectively under Kremlin control. The result could redraw the map of Europe, expanding Russia's borders by hundreds of square miles.

To win this prize, the Russians stand accused of war crimes, of starving a population, of indiscriminate bombing and civilian killings. More than 100,000 civilians remained trapped as Moscow hindered the establishment of humanitarian exit corridors. Other residents were forcibly relocated to Russia, some to cities thousands of miles east. An estimated 20,000 lives have been lost in Mariupol, and satellite images released last week showed mass graves 12 miles west of Mariupol. Mayor Vadym Boychenko called it a "new Babyn Yar" — a reference to the mass graves near Kyiv where the Nazis massacred at least 33,000 Jews.

"The biggest war crime of the 21st century was committed in Mariupol," Boychenko said Friday.

Putin's forces may find Mariupol hard to fully pacify; observers predict continued acts of sabotage from a defiant civilian resistance. But for Ukraine, a country that has held back the Russians against the odds, the city's loss represents the single biggest setback of the punishing war.

Mariupol was battle-scarred long before the Russian invasion began on Feb. 24.

After an uprising in Kyiv ousted Ukraine's Russia-friendly president in 2014, and Putin's troops invaded Crimea, the city came under direct assault by Kremlin-backed separatists. Its city hall was scorched and ruined. A few months after the successful ouster of the Kremlin's allies, a commander from what was then called the Azov Battalion — the right-wing Ukrainian unit known in the past for attracting extremists — presciently told The Washington Post: "This peace will not last. Putin thinks he is a monarch, that we must all kneel before him."

A salvo of Grad rockets struck a market to the east of Mariupol in 2015, killing 31 people. The city's airport closed for years because of its proximity to the conflict in the east. Residents kept emergency bags packed in case the city was breached again.

Yet, at the same time, renewed investment from Kyiv injected new energy into the city. Streets were fixed. Stylish bars and cozy restaurants sprang up in quirky neighborhoods lined with Soviet-era apartment blocks. Urban life bloomed anew. Wrestlers once again competed for the prize of a sheep at the annual "Great Feast," a celebration of Mariupol's place at the center of Ukraine's Greek Orthodox life. The Club 8-Bit Museum on Nielsen Street harbored a delightfully nerdy gallery of vintage electronics.

Until Russian shells struck last month — destroying the gallery and the home of its owner, Dmitry "Brain" Cherepanov.

"Russia should suffer the most severe punishment possible for what it has done," Cherepanov, 45, said in an interview on Telegram on Friday from western Ukraine, where he fled with his family. "Their soldiers just came to rob and kill us."

Serhiy Taruta, a Ukrainian lawmaker and business leader from Mariupol, said in a Skype interview from Kyiv on Friday: "There was no way to break [Mariupol's] resistance, to break its spirit." That meant the Russians had to eliminate the city physically, he added.

"It was possible to destroy our heroes only by destroying the city, and they did it from the first day," he said.

On Feb. 23, Boychenko had his last day as a peacetime mayor, holding a ceremony for smiling child figure skaters. The city council wrote on its Telegram account that "the situation in Mariupol is calm. The city is under reliable protection."

The next morning, Mariupol — and Ukraine — were under attack.

Apartment buildings were shelled. People took to their basements. Electricity in parts of the city went out, then water. The city imposed a curfew that evening. "We're not panicking," Boychenko said.

In the first days, Mariupol still felt like a comparatively safe haven. Residents of Sartana, a village just to the northeast, gathered their belongings into white plastic bags and boarded buses toward the city center. Other refugees were encouraged to shelter in the grand Drama Theater, a city landmark that opened its doors in 1960 but whose four commanding Greek pillars made it look older.

Any sense of safety evaporated quickly.

The Russians "are creating a blockade for us, as in Leningrad," the Mariupol council wrote after a week of war, referring to Nazi Germany's World War II siege of the imperial Russian city. "Putin's horde of troops is constantly shelling the city."

In the early hours of March 2, Artem Kischik was awakened by a rocket strike on his apartment building on Morskyi Boulevard in eastern Mariupol, an area dominated by a grand, long path down to the sea.

"I opened my eyes and saw my brother and mother standing and shouting at me to run into the corridor," the 19-year-old wrote in an account that he later published on Instagram. "We realized that we had to leave, but it was already too late."

Instead, he shivered with his family inside their unheated apartment. "Without any light, we began to live from dawn to dusk — going to bed at about 6 p.m. and waking up at 4 to 5 a.m.," he wrote. "But much more often we woke up even earlier because of the explosions."

Eventually, the fighting came so close that Kischik's family moved into the basement along with other residents of the apartment complex. Hunger was compounded by cold. Elderly residents started to die, leading to a macabre ritual.

"The cold prevented their bodies from decomposing, so we took them to their apartments where they used to live," he wrote. His family subsisted on occasional bowls of porridge, honey and some cans of food. His brother died during one shelling.

After the Russians bombed the city's waterworks, Nick Osychenko, chief executive of TV Mariupol, said his family resorted to ripping apart home radiators to drain them of their chemical-infused water to drink. He recalled the relief of a winter storm that sent residents into the streets to fill buckets with snow to melt for water.

Like many parts of Ukraine, particularly in the south and east, Mariupol is a largely Russian-speaking city with deep traditional and cultural ties to Russia and complicated, overlapping loyalties to Moscow and Kyiv. But the sheer brutality of the assault has turned the city decisively against the Kremlin.

"I don't think anyone but Putin could have pushed Mariupol to love Ukraine this much," Osychenko said.

On March 9, Russians bombed Maternity Hospital No. 3, where generations of Mariupol's children had been born. Pregnant women wrapped in blankets fled through the smoke and broken glass. Three people were confirmed dead that day.

"Kill me now!" one injured pregnant woman shouted the day after the attack as she realized she was losing her baby, medics told the Associated Press. Both the mother and child died.

A week later, an airstrike hit the Mariupol Drama Theater — the shelter that in the first days of the war had seemed like a haven. About 1,300 civilians were hiding there ahead of the strike, authorities said; about 300 people are thought to have perished.

As the fighting continued, not even dim basements were safe anymore. As residents sought escape, confusion and chaos ensued.

Cherepanov's Mariupol Life website is now one of several digital bulletin boards where desperate family members search for the missing. On the site, Tatyana Lomakivskaya's child wrote: "Looking for mother … born in 1939 in Mariupol … very thin, height 155-160cm." In a posted picture, Lomakivskaya wears a floral green dress. "On March 15 was alive, did not go down to the basement, walks badly, the whole building burned down," her daughter wrote. "Any information please!"

In a city with a prewar population of 450,000, the armed resistance has come down to a last stronghold inside the Azovstal steel plant. A video taken Thursday and shared with The Post showed women and children in an underground basement with a steel door. Ukrainian government officials have said there could be as many as 1,000 civilians huddling there.

The commander of the Ukrainian forces inside the plant, Maj. Serhiy Volyna of the 36th Separate Marine Brigade, vowed Tuesday in an interview with The Post to never surrender. Others who had placed their faith in Russian promises of safe passage had paid with their lives, he argued, as Kremlin's forces broke pledges and opened fire.

"No one believes the Russians," he said.

In audio messages Wednesday, he appealed for international help, saying 500 of his fighters were wounded and that soldiers were "dying underground." President Volodymyr Zelensky said at a news conference last week that there were two potential ways to end the standoff — either a diplomatic solution or one in which the besieged Ukrainian fighters are armed with "serious and heavy weapons."

So far, he said, Russia had failed to agree to a negotiated resolution.

Volyna conveyed the grim sense of a force cornered and standing alone.

"While the world is asleep, in Mariupol, the guys are dying," he said in his audio messages to The Post. "They're suffering losses. They're being bombed with heavy bombs … torn up by artillery, and they're dying underground."

The duration and ferocity of Mariupol's resistance against a much larger military have been inspiration for Ukrainians across the country. Putin said that week that Russian troops would refrain from trying to clear the steel plant, calling such an operation "impractical." Instead, he ordered his men to seal it off "so that not even a fly can get through." Some military analysts saw a measure of Ukrainian victory in that announcement, saying that Putin simply couldn't risk further losses ahead of a looming assault on other parts of eastern Ukraine.

The steel plant continues to come under fire from Russian airstrikes. In the video from inside the facility, a little boy in a gray hoodie sheltering there spoke to the camera.

"We want to get out of here alive."

The Washington Post's David L. Stern in Mukachevo, Ukraine, and Louisa Loveluck in Dnipro, Ukraine, contributed to this report.

previous coverage

• Ukraine alleges renewed attack on Mariupol plant; U.N. chief to meet Putin
• A packed train to Kyiv, bearing worried and hopeful returnees