Chants blared through speakers as a crane lifted a massive Greek flag above Syntagma Square, where Greeks converged from across the country to rally against negotiations over a name dispute between Athens and Skopje.
Hundreds of buses transported demonstrators from across the country for the "Macedonia is Greek" demonstration. Tens of thousands assembled in the city centre, with organisers claiming more than one million people would take to the streets.
"Hands off Macedonia," they chanted.
"Macedonia belongs to Greece," others yelled.
The demonstration comes two weeks after an estimated 300,000 people gathered in the northern coastal city of Thessaloniki to voice their opposition to the negotiations.
White-and-blue flags fluttered above, and throngs of demonstrators wearing traditional Macedonian garb marched in anger.
As that rally came to a close, anarchist counter-demonstrators clashed with police, and far-right protesters lit an anarchist squat on fire.
Assailants later vandalised a Holocaust monument.
Before Sunday's rally in Athens, activists carried out security patrols to protect dozens of squats in the city centre from potential attacks.
Nasim Lomani, an activist at the City Plaza squat, which provides residence to upwards of 350 refugees and migrants, said extra security precautions were taken.
"All the squats are ready to protect themselves in case of any fascist attack," he told Al Jazeera. "There are fascists coming from all over Greece so we have to be careful."
The demonstrations in Athens and Thessaloniki have drawn the participation of members of the Golden Dawn, the neo-fascist party that holds 16 seats in the Hellenic Parliament.
Last month, negotiations over the decades-old name dispute between Greece, which has a northern region called Macedonia, and the Republic of Macedonia, were relaunched.
In 1991, when Greece's northern neighbour declared independence after breaking away from the war-gripped remains of the Socialist Federal Republic of Yugoslavia, Athens and Skopje were at odds over the name.
Greece accuses Skopje of territorial designs and falsifying its historical heritage by co-opting figures such as Alexander the Great, who ruled over the ancient kingdom of Macedon.
Meanwhile, the Republic of Macedonia, which was admitted into the United Nations in 1993 as the Former Yugoslav Republic of Macedonia (FYROM), rejects its neighbours' claim to hold an exclusive right to the name.
The dispute has prevented Skopje from completing its accession into the European Unionand the North Atlantic Treaty Organisation (NATO) since the 1990s.
In Skopje, former Prime Minister Nikola Gruevski oversaw a programme to erect statues of Alexander the Great, and to name highways, buildings, sports venues and the country's international airport after Greece's historical heroes.
Current Prime Minister Zoran Zaev has expressed his willingness to rename the sites and bring down the monuments that have sparked outrage in Greece.
'Undeniably far right'
At a press conference on Thursday, the rally's organisers alleged a conspiracy against Greece's claim to the name "Macedonia", blaming Hungarian-American billionaire and philanthropist George Soros for spreading "propaganda".
Nina Gatzoulis, one of the organisers and coordinator of the World Committee of Pan-Macedonian Associations, insisted the rally was "above political parties" and not affiliated with any factions.
Gatzoulis accused UN negotiator Matthew Nimetz of harbouring anti-Greek biases, alleging a spurious history of employment at NGOs funded by Soros.
"We should love our fatherland and do everything to get it," she proclaimed. "Let us be all as one and fight bravely."
Seraphim Seferiades, a politics professor at the Athens-based Panteion University, dismissed the organisers' claims to be apolitical.
"It's undeniable that this is the far right - no matter how much they are trying to conceal it," he told Al Jazeera, alluding to the organisers' long history of far-right political activity.
Seferiades argued that the size of the Thessaloniki rally indicates a "real advent of nationalism, this is the first stage of a real Golden Dawn-like resurgence".
For its part, Golden Dawn leaders have accused the Syriza-led government of national betrayal. On Saturday night, party leader Nikolaos Michaloliakos urged a crowd of 600 supporters to topple "the anti-Greek government".
"Blood, honour, Golden Dawn", the far-right demonstrators chanted, waving burning torches in the air and burning Macedonian flags.
'The real enemy is in the banks and ministries'
While Greece's far right sees an opportunity in the heightened tensions, other parties, such as the right-wing New Democracy party, have adopted an unclear stance on the demonstrations.
New Democracy leader Kyriakos Mitsotakis urged followers to steer clear of last month's Thessaloniki rally, but other party officials have expressed public support for the protests.
In the lead-up to Sunday, Mitsotakis said he respects everyone's personal decision to attend the rally, and many New Democracy officials were expected to be present.
Elsewhere on Sunday, hundreds of anti-fascists - among them anarchists, socialists and others - held a counter-demonstration in the city centre.
Thousands of police officers were deployed throughout the city, and blocked streets leading to the Syntagma Square protest in order to prevent clashes between the two sides.
"In Greece, Turkey and Macedonia, the real enemy is in the banks and the ministries," the anti-fascists chanted in unison.
Others burned the Golden Dawn flag, taunting nationalist demonstrators who were cordoned off by heavily-armed riot police.
Skirmishes between anti-fascists and police broke out on Sunday.
Over the weekend, flyers were posted on the doors of homes on several streets in Exarchia, a neighbourhood that serves as a stronghold for anarchists and leftists, warning of potential far-right attacks.
Petros Constantinou, national director of the anti-fascist group Keerfa, said the Greek far right has failed so far, in an apparent effort to use anger over name negotiations, to rebuild its support base.
"Politically, what the right wing is trying to do in its relation to the far right is to stop the ongoing shift of the population to the left," he told Al Jazeera.
"When we say this demonstration is a greenhouse for neo-Nazis, it's because of nationalism and the attempt to deny the right of the people to exist [in Macedonia] and enjoy self-determination," Constantinou added.
"I don't believe we are in the position to see people go back to the right wing. They still believe in their struggles, their strikes and resistance."
Source: Al Jazeera