BANGKOK — They gathered at a monument celebrating Thai democracy. They raised their hands in defiance below a giant image of the king dressed in coronation regalia.

At least 10,000 protesters, many first-time participants in political rallies, gathered in Bangkok on Sunday (Aug 16), demanding change in a country where military tanks have tended to shape politics more than the ballot box has.

The nearly eight-hour protest, which filled a broad avenue in the heart of the city with black-clad people, was the largest rally in Thailand since a coup in 2014, one of a dozen successful putsches in the country in the last nine decades.

A state of emergency instituted because of the coronavirus made the demonstration technically illegal, and every participant could have been arrested simply for showing up. The police stood by, however, some idling behind a Mercedes-Benz showroom.

Thailand’s growing protest movement, which was set off by student activism last month, has since gained broader support.

While Thailand has escaped the brunt of the pandemic, it has been pummeled economically, and millions are out of work. With Mr Prayuth Chan-ocha, the retired general who choreographed the last coup, still leading the country as prime minister, Thais have intensified calls for a new political order.

“We have had many political divisions in our country but now, no matter what our backgrounds, many of us are united in questioning the legitimacy of this government,” said Ms Nuttaa Mahattana, a democracy activist. “Look at who’s here, many different types of people.”

The protest leaders have demanded a new constitution, one not written by the military, as the current charter was. They have called for parliament to dissolve. They are pleading for the protection of human rights at a time when vocal critics of the military and monarchy have disappeared and been killed.

And they say they will keep gathering if their aims are not met.

“We don’t hate the country, but we hate you, Prayuth Chan-ocha,” Benjamaporn Nivas, a 15-year-old student, sang from the stage she shared with others, taking the melody of a children’s song and adding new lyrics.

“We don’t want dictatorship.”

Sunday’s protest took place at the Democracy Monument, which was built to commemorate the 1932 bloodless revolution that ended absolute monarchy in Thailand. The country is now a constitutional monarchy, but some of the protest leaders have accused the palace of breaching the terms of that form of government.

King Maha Vajiralongkorn Bodindradebayavarangkun spends little time in Thailand, living most of the year in Europe. He has consolidated financial and military power, bringing crown coffers and influential army units under his control.

After some protesters called for checks on the palace’s power in rallies last week, a rare challenge in a country where lèse-majesté laws can land critics of the crown in jail for up to 15 years, authorities pressured the movement’s leaders to keep the monarchy out of their speeches.

But as Sunday’s rally stretched into the night, after speeches on labuor law, student haircuts and rights for gay, lesbian and transgender people, Mr Arnon Nampa, a young human rights lawyer, took to the stage and defied any such request.

Earlier, a laser had projected a hashtag that asked in Thai, “why do we need a king?” onto the white face of the Democracy Monument.

The authorities “have asked us to stop dreaming,” he said, referring to “the biggest dream of seeing the monarchy stay alongside Thai society,” rather than floating above it unbound by legal charters.

“I am announcing here,” he added, “that we will continue dreaming.”

The demonstration took place under a large photograph of the king during his 2019 coronation, when he was formally presented with a 16-pound golden crown and a fortune that makes him one of the world’s richest royals.

Above the orderly rows of protesters was also an oversize picture of Queen Suthida Vajiralongkorn Na Ayudhya, the king’s fourth wife, in a military uniform. A former flight attendant, she has been given the military rank of general in the king’s bodyguard corps.

A pro-royalist counterprotest gathered Sunday as well. Its numbers were small.

Even before the protest kicked off, the Thai security apparatus had begun harassing those who might want to speak out. Mr Arnon was arrested on sedition charges last week. He and another activist are also facing lèse-majesté complaints.

Early Sunday morning, Mr Pongsak Phusitsakul, an opposition politician whose party was dissolved before it was able to contest elections last year, said his dogs alerted him to six plainclothes police officers who went to his home, he said, to intimidate him before the rally.

“I’m used to it,” he said. “But I’m worried about the youth, what they will face and what their parents and families have to face.” THE NEW YORK TIMES