Vatican City also flew its yellow-and-white flags at half staff in solidarity.
The nation of 60 million people has recorded nearly a third of all fatalities caused by COVID-19 across the world.
The day of mourning marks a month in which Italy saw more deaths from a single disaster than at any time since World War II.
On Monday the country reported 812 deaths, lower than the record 969 on Friday — the highest daily toll recorded anywhere in the world.
The coronavirus infection was first detected near the northern financial hub Milan in late February.
It spread and overwhelmed hospitals with critically ill patients thereafter.
The virus “is an injury that hurt the whole country,” Rome mayor Virginia Raggi said after a priest read a prayer for the dead and the nation observed a minute’s silence.
“Together, we will get through this,” she said at a ceremony held outside Rome’s city hall.
The Italian government imposed an unprecedented lockdown three weeks ago to help stem the spread of a virus that has now officially infected more than 100,000 people in the country.
On Monday the government decided to extend the shutdown until at least mid-April.
The financial cost of the forced shutdown of almost all businesses threatens to send Italy’s economy — the European Union’s third largest last year — into its deepest recession in decades.
Stores and restaurants are not expected to start opening until at least May and no official is willing to predict when life might return to the way it was just a month ago.