Old friends from Argentina reunited in New York. Five died together in a terrorist attack.

The childhood friends from Argentina had been planning the trip to New York City for years.

The men all hailed from Rosario, Argentina’s third largest city, about 185 miles northwest of Buenos Aires. As teenagers, they had bonded in the halls and classrooms of the Instituto Politécnico, a technical high school in Rosario, and graduated together from there in 1987.

Through the decades — despite job changes, marriage, children, moves to far-flung corners of the world — they remained close friends. And on Saturday, eight of the former classmates gathered to fly to the United States to celebrate their 30th graduation anniversary.

They were in their late 40s now, firmly in the realm of middle age. But as they posed for a photograph just before their departure, the old friends slung their arms over one another and grinned like schoolkids. They donned matching white T-shirts emblazoned with the same word: “LIBRE.” Free.

It is unclear when exactly they arrived in New York; they had planned to stop in Boston, to meet up with another former classmate. But what is certain is that on Tuesday — a beautiful, brisk fall afternoon in Manhattan — the men rode bicycles along a bike path flanking the Hudson River.

As they pedaled along the West Side Highway, a white rented Home Depot truck turned onto the path as well.

The truck would soon plow into a crowd of pedestrians and cyclists, killing at least eight people — including five of the Argentine men. At least one other former classmate from the group was injured.

The Home Depot truck would later careen into a small school bus, injuring four more inside, officials said. After leaving behind a trail of chaos, the 29-year-old driver of the truck was shot and arrested by police, ending what authorities described as a terrorist attack. Officials said the suspected attacker, Sayfullo Saipov, left a note pledging his allegiance to the Islamic State. New York Gov. Andrew M. Cuomo (D) said Saipov was believed to be a lone wolf who was “radicalized domestically” after moving to the United States from Uzbekistan six years ago.

The brazen daytime attack, which took place less than 10 blocks from the World Trade Center and 9/11 Memorial, sent shock waves through the city — but also thousands of miles away, as friends and family in Argentina coped with the sudden loss of five of their own.

The Argentine Foreign Ministry identified the five dead Argentine nationals as Hernán Diego Mendoza, Diego Enrique Angelini, Alejandro Damián Pagnucco, Ariel Erlij and Hernán Ferruchi. It added that a sixth member of the group, Martin Ludovico Marro, suffered injuries and was hospitalized in the Presbyterian Hospital of Manhattan. He is in stable condition, the government said, citing medical officials.

“They were five young entrepreneurs, model citizens in Rosario society,” said Argentina’s president, Mauricio Macri, in Buenos Aires. “We all must stand together in the fight against terrorism.”

The mayor of Rosario declared flags to be flown at half-staff for three days of mourning, according to the city’s local newspaper, La Capital.

It was Erlij, 48, who had organized the reunion trip for the classmates, paying for those who couldn’t afford it, according to Mary Bensuley, a longtime family friend. Erlij was a well-known Argentine businessman who owned Ivanar, an iron and steel works company.

“I can say the family has a great spirit of solidarity,” Bensuley told The Post. “Their trip was to mark the 30-year anniversary after graduation . . . They’re great people. They have a good economic position, and they were always offering to help.”

She described Erlij’s family as “devastated.” Like many Argentines on Wednesday, Bensuley was having a hard time processing the motivation for the attack.

“Here, everyone lives in peace, and religion has never been a big subject of conversation,” she said in a Facebook message. “There are big debates about politics and soccer, but religion? Not really. We’re Catholics and we have Jewish, atheist and Mormon friends. Muslim friends, too. Our pain is for the innocent and unjust deaths of people who have nothing to do with the craziness that brought people trapped by their fundamentalist ideas to cause such terrible damage.”

Erlij was at the airport in Rosario on Saturday, but did not depart with the group, instead catching up with the others in New York on a private flight the following day, according to the Argentine newspaper Clarín.

Erlij’s friend, Luciano D’Amelio, told The Washington Post he was successful and generous, a gym buff who made time for workouts despite his busy life. Erlij was Jewish, though his wife was not, D’Amelio said. The couple had three children, she said.

“I’m still in shock,” D’Amelio said in a Facebook message. “The incident really hit us. Never in our wildest imaginations did we think something like this could happen.”

Jose Lo Menzo, another one of Erlij’s friends, described him as an “excellent person and father” who was also very intelligent.

"[Erlij] studied in a public, middle-class school, and he managed to become a successful businessman, without forgetting about his friends,” he said. “It is a loss without meaning.”

At least two of the victims, Ferruchi and Angelini, were architects, according to La Nacion.

Ornee Pagnucco, 18, one of the three daughters of victim Alejandro Pagnucco, told The Post the 48-year-old and his friends had been planning their reunion trip for more than a year. Alejandro Pagnucco worked for a construction materials company and had never traveled much, but he saw New York as iconic. Visiting the city, she said, had been his “dream.”

After her father left, he sent photos of his hotel room and selfies of him walking through New York’s streets, Ornee Pagnucco said. She added she knew terrorist attacks had happened there but never considered them a serious risk.

“We’re shattered,” she said. “It’s been really hard.”

Early Wednesday, a friend of Pagnucco posted a Facebook tribute to “a good student and son, a great worker.”

"[The attacker] did not care who you were, did not care about the three beautiful daughters you have. Nor your dear brothers,” Gustavo Repizo wrote on behalf of his late friend. “You destroyed a family that was not interested in the religious or monetary problems of the world.”

“Picho,” Repizo added, using a nickname for his friend, “was a person of peace.”

Cecilia Piedrabuena, the wife of Ariel Benvenuto — one of the Argentines who survived the attack — told Rosario's Radio LT8 her husband had been bicycling behind the others when “he felt something go past by him.”

“He saw [the attacker's van] veer toward five of his friends,” Piedrabuena told the radio station. “He said it was going at more than 150 kilometers per hour (93 mph) … terrible.”

Her husband had called her from New York shortly after the attack; she listened to him in disbelief, she said, unable to grasp what had happened at first because it wasn't yet on the news.

Piedrabuena described the group of Argentines as being the “10 closest friends from high school.” They saw each other frequently, she said, at least a few times a year. They had planned the trip for this year because Erlij had offered to pay for those couldn’t afford it, she told Radio LT8.

Their plan that day, Piedrabuena said, had been to bicycle through Central Park, and then over the Brooklyn Bridge.

“They didn't make it,” she told the radio station.

Estefania Garcia, a Rosario resident and alumna of the high school, told The Post she knows Marro, the man currently hospitalized for injuries from the attack, and spoke with his sister-in-law Tuesday night.

Though details behind the photo of the men in matching T-shirts were not yet confirmed, Garcia said it was “no coincidence that they wore T-shirts with the inscription ‘free.’ ”

“Freedom” is one of the essential values taught at their alma mater, Garcia said. She described it as a tightknit community that leads to lasting friendships. It has a demanding curriculum, with long days of workshops, meaning classmates become very close. She said she was not surprised to hear that a group of alumni were still close friends, three decades after graduating. Garcia herself remains very close with her friends from the high school.

“We all love it,” she said. “Graduates live all over the world.”

Marro is a longtime U.S. resident living in the Boston suburb of Newton, and he works as a biomedical researcher at Novartis Institutes in Cambridge, according to Newton City Council member James Cote.

Cote, a Republican, said Marro hosted a fundraiser for him last week that was also attended by Massachusetts Gov. Charlie Baker (R). Cote said Marro and his wife, an architect, “are not political people” but had offered to host the event because Marro’s wife is a friend of Cote’s wife, who is also from Argentina.

Marro has two sons in elementary school in Newton, Cote said, and Marro coaches soccer.

“They are very nice, very quiet people,” said Cote. “They were just in the wrong place at the wrong time.”

The Argentine government expressed its “sincere condolences” and said its consulate remains in contact with police authorities, hospital staff and the victim’s relatives in Argentina.

“We accompany the families in this terrible moment of deep pain, which all Argentines share,” the government statement read.

On the Instituto Politécnico campus, students planned a candlelight vigil Wednesday night in memory of the group of “Poli” alums who died.

“It hurts us as students, because they took the same steps as us,” Agustín Riccardi, president of the student center at the Instituto Politécnico, told The Post. “We are all hurting. It’s a very close community. Everyone has a family member who went to ‘Poli.’ ”

Ricardo Berlot thought it was a bad joke Wednesday morning when he read a WhatsApp message saying five of those killed in the Manhattan attack were “rosarinos” — from Rosario, his home town. In fact, they were from the same school he had graduated from 30 years earlier and where Berlot was now a teacher. The victims had been students in his computing class.

“What happened affects us as if we were all of one body,” said Berlot, 58, speaking to the press outside the school on Wednesday. “At this institution, we create strong bonds . . . It's absolutely normal that former students get together for an 'asado' [Argentine-style barbecue] and to talk about the school.”

On Wednesday afternoon, New York police identified all eight victims. The three others killed in the attack were Anne Laure Decadt, 31, of Belgium; Darren Drake, 32, of New Milford, N.J.; and Nicholas Cleves, 23, of New York.