Question

Which region did the Byzantine empire control for the longest period

Answer 1

Italy and the Adriatic coastlines were controlled by the Byzantine empire for the longest period.

The Byzantine Empire also known as the Eastern Roman Empire was the  longest-lasting medieval power which lasted from 330 to 1453 CE. Constantine I founded its capital at Constantinople, and the size of the Empire varied over the centuries since it had territories located in Italy, Greece, the Balkans, Levant, Asia Minor, and North Africa.

Answer 2

Italy and the Adriatic coastlines 

I hope this helps, have a great day ;)