The demonstration was organized by the League, Brothers of Italy and Go Italy parties, to protest against the coalition government led by Prime Minister Giuseppe Conte.
The event took place on the anniversary of a referendum on replacing the monarchy with a republic after the Second World War.
Protesters carried a large national flag along the Via del Corso, leading to the Piazza del Popolo in Rome’s historic center.
Many activists were not wearing face masks, which are compulsory in Italy in situations where social distancing cannot be observed.
With more than 233,000 confirmed cases, Italy is one of the countries hardest hit by the coronavirus pandemic. The government only recently decided to gradually lift restrictions it had imposed in early March to rein in the contagion.