A heat wave sweeping much of Europe showed few signs of relenting on Monday, when temperatures soared past 100 degrees Fahrenheit, or 37.8 Celsius, in many places in the south.

In Italy, heat warnings were issued for 16 cities. And in France — still scarred by a 2003 heat wave that killed thousands — the prime minister canceled a trip to monitor the effects of the weather.

How bad is it? A nuclear reactor in southern France had to shut down, because discharging its heated water into an already-overheated river would have endangered wildlife.

Through it all, Europeans tried their best to bear up, especially in places where air conditioning is still a luxury, or frowned upon. Some people worry about the pollution it causes; some older Italians just believe it’s bad for health.

Governments tried to help, in some cases putting restrictions on outdoor work and sending municipal workers to check on elderly residents.

Tourists still bent on being outdoors struggled. In Rome, visitors wilted at cafes even as they were spritzed by outdoor misting fans. Some sought respite from the heat in cavernous ancient monuments, which didn’t always help.

“It was cool looking at it, but not in temperature,” Eileen Santos, a tourist from the San Francisco Bay Area, said walking out of the Pantheon. Across the square, tourists filled water bottles from jets of water spouting from a 16th century fountain. Lines formed at some of the more than 3,000 water fountains that Romans affectionately call “nasoni,” or big noses.

Rome is one of the 16 cities that had a “level 3 warning” signaling “possible negative effects on healthy and active persons, not only those at risk.”

“In some places in Europe we are experiencing temperatures that have never been recorded before, so it is really unusual,” said Carlo Buontempo, director of the Copernicus Climate Change Service, based in Spain. But he added that this was “not surprising, because with climate change, we’re bound to see more intense, longer, and more frequent heat waves, and that’s exactly what we’re seeing.”

In France, suffocating heat gripped most of the country, but spared the country’s northernmost edges. Temperatures, which exceeded 104 degrees Fahrenheit, or 40 Celsius, in some areas, will peak on Tuesday and Wednesday, according to the national weather forecaster.

The government held a crisis meeting on Sunday evening and reminded employers of a decree that goes into effect tomorrow that forces companies to change employees’ working conditions — having them start earlier in the day, for instance, when it’s cooler. Cities around the country extended opening hours for parks and made entry to swimming pools and museums free.

The Italian Health Ministry enlisted a popular television host for a commercial on best practices to beat the heat. In Rome, municipal pools are free for anyone over 70.

But for those people fortunate enough to be near water, the beach remained the number one option, when they could find space.

In Carcavelos, Portugal, 15 kilometers from Lisbon, the beach was so packed on Sunday that Camila Guerra, a 37-year-old social worker, had struggled to find a spot for herself and her two children. “Our house doesn’t have air conditioning, and we all woke up sweating,” she said. “We knew we had to go to the beach.”

On Sunday, Portugal’s provisional record high for the month of June was set in Mora, where temperatures soared to 46.6°C (115.9°F), forcing farm workers to alter their shifts so they could stop working by 2 p.m. “It’s impossible to stay out in the sun beyond that time. The heat is dry and scorching, you can barely breathe,” said Vítor Dias, deputy chief of the local fire brigade.

In Greece, the extreme heat, which reached 40C in Athens on Friday and touched 43 in the southern part of the country, stoked dozens of wildfires. The fires, along with the heat, have abated, but on Monday, civil protection authorities issued a notice of a very high fire risk in Athens as well as several Greek islands.

In general, the elderly are the most vulnerable population. Residents in one care home in Mora, Portugal, were forbidden from going outdoors during the day, while city officials have been making the rounds of the elderly who receive at-home assistance, to “advise them on how to cope with the heat,” said Paula Chuço, the mayor.

A provisional record for the highest June temperature ever recorded in Spain, 46C, was registered over the weekend in El Granado in southwestern Spain, the 45th record to be broken this year, according to the Spanish State Meteorological Agency.

The Carlos III Health Institute estimates that approximately 1,300 people die each year in Spain due to high temperatures. Yolanda Díaz, the country’s minister of labor, said on her BlueSky account that “when an orange or red heat alert is issued for adverse weather, you can reduce or modify your work day.”

Sales were up in Madrid for ‘abanicos,’ the traditional Spanish hand fan. One purveyor, the Casa de Diego, on the Puerta del Sol, the city’s largest square, said business was booming. Arturo Llerandi, the sixth generation to run the family business, said the fans were eco-friendly because they don’t pollute.

In the square, large tarps provided visitors with some shade. Some people made a beeline for the Apple Store, which a security guard described as an informal “climate shelter” because of its strong air conditioning.

Among those suffering from Spain’s heat was U.N. Secretary-General António Guterres, who posted on X from Seville, where the temperature hit 42.6C (108.7F).

“Extreme heat is no longer a rare event — it has become the new normal,” he wrote. “I’m experiencing it firsthand in Spain during the Financing for Development Conference. The planet is getting hotter & more dangerous — no country is immune. We need more ambitious #ClimateAction now.”

In the Paris metro, Zsuzsanna Pajor, 60, was holding an electric fan to her face to cool off as the station’s overhead speakers crackled with warnings to stay hydrated. Half of the French capital’s metro system does not have air conditioning, and Ms. Pajor, like many in Paris, does not have AC at home either.

“I used to have a fan during the night but it would leave me with a stuffy nose in the morning, and I couldn’t sing anymore,” said Ms. Pajor. As a freelance music teacher, she said, that was not an option.

At an outdoor market in the central Campo de’ Fiori in Rome, Cristina Campaci fretted about the state of her vegetables, which she said wilted “before your eyes,” even as she tried to remain resilient.

“We’re used to the heat, but this is very tough,” she said. “We have a pail of water, we splash ourselves every once in a while. And then, with a smile, we go on.”

Aurelien Breeden and Ségolène Le Stradic contributed reporting from France; Tiago Carrasco from Portugal; José Bautista from Spain and Niki Kitsantonis from Greece.