This hall is named after Cesare Maccari (1840-1919), the artist who decorated it after winning a contest of the Ministry of Education in 1880. On the ceiling, four medallions around a central motif symbolising Italy depict allegorical figures representing trade, agriculture, the arms, science, humanities and the arts. A sentence by Guicciardini and another one by Machiavelli are written along the frieze around the ceiling.

The walls are painted with scenes from the history of the Roman Senate. On the right, Appius Claudius the Censor can be seen while he is led into the Senate to convince the Romans not to accept the humiliating peace conditions imposed by Pyrrhus's ambassador Cineas. On the adjacent wall, between the windows, there is a fresco depicting Marcus Papirius bravely seated motionless during the Gallic invasion, and another one depicting the Samnites trying to bribe Curius Dentatus to convince the Senate to make peace. On the following wall, there is a fresco depicting Cicero who delivers his oration against Catiline, who, isolated by the other Senators, listens from his seat. The last fresco shows Atilius Regulus who, sent back to his country after being captured in the Battle of Tunis by the Carthaginians to negotiate with Rome on condition that he considers himself a prisoner, is going back to keep his word although he knows he will be certainly put to death.