At midday on 17 March, 150 shots will be fired from the cannon on the Janiculum hill. In what is sure to be the loudest celebration of Rome's festivities in honour of the 150th anniversary of the unification of Italy, those within earshot will be left in no doubt as to the age of the republic.

Fired daily at noon, the cannon has been a feature of Roman life since 1 December 1847 when Pope Pius IX ordered that it be fired to alert the city's church bells to begin ringing.

The tradition began at Castel S. Angelo, before the cannon was moved to Monte Mario and finally in 1904 to its present position on the Janiculum hill. Its use was interrupted by the outbreak of war in 1939 but 21 years later, thanks to an appeal by the media and the residents of Rome, the tradition was reinstated on 21 April 1959.

Known by the military personnel who fire it as the