The demonstration was organized partly through a call on Facebook, The New York Times reported. Protesters gathered in the Piazza della Repubblica next to the main railroad station for a march through the city.
"This started with civil society, people who are touched by problems like unemployment and the economy and the environment and want things to change," Elisa Tottone, a Roman teacher, told the Times. "Berlusconi is not dealing with Italy's real problems. He only cares about his own."
Police estimated the size of the crowd at 90,000, although organizers gave much higher figures.
While the demonstration was aimed primarily at Berlusconi, some marchers said they are also angry at the opposition. Berlusconi, a media tycoon as well as a politician, appears to have a lock on power in spite of sex scandals and accusations of corruption.