Italian climate activists from the Last Generation group used fire extinguishers to spray orange paint on the facade of the famous Palazzo Vecchio in Florence on Friday.
The action, conducted by two activists, lasted only a few minutes and the paint is washable, the group said. The 14th-century building houses the city's town hall.
Photos and videos showed the activists pulling the paint-filled fire extinguishers out of their backpacks and spraying the historic façade. Law enforcement officers were immediately on the scene and stopped them. While the two were being led away, passers-by reacted to the action, some of them gruffly and with insults.
Clean up began immediately after the spraying, with Florence Mayor Dario Nardella taking part in the cleaning effort.
"These are barbarians," he told the Italian Ansa news agency. "This is no way to protest."
The Palazzo Vecchio originally served as the seat of the Florentine city parliament. In the 19th century, it was also the seat of the Italian Chamber of Deputies for a few years.
Today, the building houses the Children's Museum of Florence, the offices of the municipal administration and the Hall of the Five Hundred.
According to the group, the action was directed against the climate policy of the Italian government, which, in their view, does too little to combat climate change.
The activists argued in a statement that the building remained unchanged, but "those who inhabit it today have lost the vision of responsibility for the future of their community."