The arrests are linked to fraudulent nods for city contracts, including tenders for the 2010 restoration of the Julius Caesar wing of the palace where city councillors meet, Rome's financial police said in a statement.
A senior official from Rome's cultural heritage agency, which manages the capital's archeological sites, was among those arrested, police said.
The official is alleged to have given preferential treatment to businessman Fabrizio Amore, who is already under investigation as part of a vast probe launched in December into allegations that a mafia network skimmed off public funds for years.
More than 100 people, including former mayor Gianni Alemanno and prominent business figures, are under investigation in the so-called "Mafia Capitale" probe.
Police in charge of the investigation believe the network was run by Massimo Carminati, a notorious one-eyed underworld figure with links to the far right.
Last week, Italian police arrested 44 people accused of dealings with Carminati, whose gang thrived on rigging Rome public contracts on everything from garbage disposal to park maintenance.
Officers cuffed local politicians from both the left and right, including regional councillor Luca Gramazio from Silvio Berlusconi's Forza Italia party, accused of serving as a go-between for corrupt businessmen and the mob.
Tuesday's fresh arrests caused a stir in the Italian capital, with Marco Vincenzi, head of the local wing of the centre-left Democratic Party, resigning and the opposition calling for the resignation of mayor Ignazio Marino.
Some opposition figures even called for Rome's municipal government to be dissolved, charging that it has been "infiltrated by mafia".