Cannone di Mezzogiorno

Roma Capitale states that since 1904 a howitzer has been fired with a blank charge at exactly noon each day below the Janiculum Belvedere, and that the tradition goes back to Pius IX, who instituted the service in 1846 to prevent confusion over the hour; before reaching the Janiculum the gun was fired from the towers of Castel Sant'Angelo and then from Monte Mario. it.wikipedia gives the Janiculum date as 24 January 1904 and the institution of the noon signal as 1847.