Tens of thousands of flag-waving Greeks rallied in Thessaloniki Sunday, demanding Greece never compromise on the name Macedonia for its northern province.
Greece and the former Yugoslav Republic that shares the same name have been feuding over who gets to use it since Macedonia became independent Yugoslavia in 1991.
Police put the turnout for Sunday's march at 90,000 while organizers say it is much higher.
Some of the protesters wore costumes from the period when Macedonia was ruled by the ancient Greek King Alexander the Great.
They say allowing the neighboring country to use the name Macedonia insults Greek history and implies a claim on Greek territory.
Sunday's march was largely peaceful. But police quickly intervened when scuffles broke out between far-right extremists and anarchists who held up banners denouncing nationalism.
Greece has blocked Macedonian efforts to join the European Union and NATO because of the name dispute.
But United Nations negotiator Matthew Nimetz said last week he is "very hopeful" a settlement is near.
Greek Prime Minister Alexis Tsipras tells the Ethnos newspaper "If there is an opportunity for a solution, it would be a national stupidity not to make good use of it."
The country of Macedonia is officially known at the U.N. as the Former Yugoslav Republic of Macedonia.