I'm travelling using a booked Etihad ticket from London to Abu Dhabi with transfer in Rome. I'll arrive at FCO at terminal 3 at 20h30, and I'll depart from FCO terminal 1 at 22h00. I have been told by Etihad that they will handle checked luggage through. What is the walking time between these terminals and are there security checks required?
In my experience, and with your luggage checked through as mine was, the 1.5 hour time should be sufficient. Walking from 3 to 1 is a bit circuitous and there are security checks, but it is well signed. Our connection was much tighter than yours, 50 minutes, and we made it with only a slight bottleneck in the security line. Our arrival was mid-morning, which can be busier than when you'll land at FCO. I found the terminal maps helpful to navigate from Terminal 3 arrivals to the departures in Terminal 1. FCO also has a live flight tracking tool which you can use to double check your arrival and departure gates and times.