The Italian capital was preparing Friday for a high-security lockdown as 27 heads of state or government head to Rome for the European Union's 60th anniversary celebrations.
Snipers will be positioned on rooftops, drones in the skies, and 3,000 police officers on the streets around the centre of the Eternal City Saturday as Italy takes no risks following an attack this week in London claimed by the so-called Islamic State (IS).
Most of the commemorations will take place on the Capitoline Hill, the political and religious heart of the Roman empire in ancient times and the modern-day city hall, where the founding countries signed the Treaty of Rome in 1957.
Organisers say security will not have been this tight since the funeral of pope John Paul II in 2005, with police on the alert not only for lone wolf attackers but also violent anti-Europe demonstrators.
According to Italian media reports, the security services have had help from Britain's Scotland Yard in bolstering the city's defences.
Some 30,000 protesters are expected to take part in four separate marches -- both pro- and anti-Europe -- throughout the day, with two coming from opposite ends of town to meet at the Colosseum.
The "Euro Stop" march in particular will be closely monitored amid fears it could be infiltrated by "black bloc" groups of far-left or far-right anarchists from Germany, Greece or France.
Security checks are already in place at tourist sites such as Vatican and Pantheon, as well as at railway stations and major airports across the country.
The capital will become a no-fly zone for the day, lorries and trucks will be banned from the centre and several metro stations will close.
Access to two areas around the celebrations -- so-called blue and green zones -- will be tightly controlled.
The roads around the Capitoline Hill, where the leaders will sign a declaration on Europe's future, will be closed to all but foot traffic from 0:30 on Saturday morning, while those entering the larger "buffer zone" will have to undergo tight security checks.
A new surveillance system has been installed in the surrounding streets for the occasion and scooter helmets and ski masks often worn by black bloc rioters to protect their identities have been banned.
Tourists without the necessary permit to reach Rome's ancient gladiator arena need not fret: the Colosseum will be closed in any case.
Many Romans meanwhile appeared to have decided to get out of city for a long weekend leaving normally teeming streets deserted and some classrooms half-empty on Friday.