Italy is very specific about when vehicles must have winter/snow tyres (or chains in the vehicle) and when owners are permitted to change them back to summer tyres.
Winter/snow tyres must be on by 15 October and summer tyres can be on any time after 15 April.
Why have different tyres anyway? Why not just use winter ones all year round?
As an ignorant Australian, I asked this same question a few years ago...
Apparently winter tyres make your car less fuel efficient so it pays to put your summer tyres on as soon as you can.
Since we spent April in Australia, we must be the only people in Italy who changed their tyres in late May!