Thirty seven people were arrested on Tuesday and dozens more are under investigation for alleged ties to the criminal organization, Italian media reported.
The home of Alemanno, who was Rome's mayor from 2008 to 2013, was one of a number of locations searched in the capital, Ansa said.
Investigators from Italy's special operations division (Ros) also collected documents from Rome city hall and the Lazio region offices.
Authorities have additionally ordered €200 million worth of assets to be seized, Ansa said. Italy's financial police (Guardia di Finanza) were not able to comment on the investigation when contacted by The Local.
The criminal network is thought to be led by Massimo Carminati, a former member of the terrorist cell Nar (Armed Revolutionary Nuclei), which was responsible for the deadly Bologna bombing in 1980.
Riccardo Mancini, who used to work at real estate company Ente Eur, is also said to be under investigation.
The litany of crimes gang members are accused of include corruption, extortion, bid rigging, false accounting and money laundering.
Investigators documented a corrupt system of assigning contracts from city hall, in some cases involving the management of immigration welcome centres, Ansa said.