The couple had sex one mid-afternoon in the castle's gardens - right in front of a police station - Il Messaggero reported.
But instead of being snarred by police, the lovers - a 37-year-old from Foggia and his Roman girlfriend, 39 - were spotted by an elderly lady, who immediately reported them.
A policeman sent to verify the situation was able to confirm the woman's report, and the couple were arrested.
They appeared in court on Thursday, where judge Francesca Giordano handed down the sentence for "obscene acts in a public place".
The lawyer defending the couple, Marco Lombardi, said they would be appealing the decision.
“I find it incredible that they have prosecuted two lovers, when far worse crimes happen every day,” he was quoted in Il Messaggero as saying.