BRASILIA (Reuters) - The wide open spaces of Brazil’s futuristic capital were hailed as a sign of the vast, fast-growing country’s optimism for the future when it was inaugurated in 1960.

People take pictures of messages written on protective fences set up to separate the demonstrators who are for and against the impeachment of President Dilma Rousseff in Brasilia, Brazil April 16, 2016. REUTERS/Paulo Whitaker

Now a steel barricade 2 meters (6.6 feet) high runs like a scar down Brasilia’s central esplanade outside Congress to stop a divided people from coming to blows.

The barrier, which is 1 km (0.6-mile) long, will separate rival demonstrators on Sunday when Congress votes whether to impeach leftist leader President Dilma Rousseff on charges of manipulating budget accounts.

For many, it has become a symbol of the deep divisions in Brazilian society and goes against everything the utopian capital, designed by architect Oscar Niemeyer, was built to represent.

“Brasilia was planned as an open space with no division, where you could see as far as the horizon,” said Rogerio Rosso, chairman of a committee that recommended the lower house vote to impeach Rousseff. “The fence is bad, but if there are security worries, we have to have it.”

The day before the vote, an uneasy calm hung over the vast esplanade overlooking the sleek, white Congress building and rows of block-like ministries. Hundreds of thousands of protesters are expected on Sunday.

Red banners in support of Rousseff were draped across one side of the wall. “Congress, the people are watching. There will be no coup,” read one, using the term the ruling Workers Party uses to denounce an impeachment it argues has no legal grounding.

Most Brazilians - 61 percent according to the latest poll - support impeachment, with their country mired in its worst recession since the 1930s and the government embroiled in a corruption scandal centered on state-run oil company Petrobras.

One, 33-year-old Guilherme Teles stood on the other side of the wall, the gold and green flag of Brazil wrapped around his shoulders.

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Out with his wife and two young children, he said he wanted his kids to get a feel for the historic moment - it would be the first time Brazil has impeached a president for more than three decades. But he won’t be coming back on Sunday because he is afraid there will be violence.

“Some people are threatening to use parts of the fence as weapons,” he said.

COULD INFLAME TENSIONS

Governor Rodrigo Rollemberg’s decision to erect the barricade to allow both pro- and anti-impeachment groups to occupy the city’s most central square has been criticized across the political spectrum amid fears it will enflame tensions.

“It’s sad but the wall is necessary,” said a young policewoman in aviator glasses and pastel pink lipstick, one of a group of officers using the wall’s thin strip of shade to shelter from the ferocious midday sun. “I think it’s going to get violent.”

If impeachment is approved by two-thirds of the lower house, the Senate will then have to vote whether to put Rousseff on trial. If she loses that vote, she will be suspended and replaced by Vice President Michel Temer, ending 13 years of Workers’ Party rule during which millions of Brazilians rose out of poverty.

When Brazil last voted to impeach a president in 1992, things were different.

The country was united both on the street and in the lower house where only 23 of 503 congressmen voted against impeaching President Fernando Collor de Mello on corruption charges.

The jovial crowds that partied late into the night then were a mix of red and gold and green. Sunday’s vote will be closer, the reaction on the street splintered.

Across town, thousands of Rousseff supporters have set up camp. Activists, bused in, are sleeping in tents and being fed by volunteers.

At a rally in the central marquee, Jose Rosalba dos Santos, 50, said he will take to the esplanade on Sunday but thinks things will remain calm.

As he waved his red flag, a rousing speech came over the tannoy. “There won’t be a coup ... There’ll be a battle,” it said.