Answer:
Balkan Peninsula
Step-by-step explanation:
The peninsula that Rome controlled and was located east of it was the Balkan Peninsula. The Balkan Peninsula turned out to very valuable territory for the Roman Empire, and later for the Byzantine Empire, but it didn't came easy into their possession. While Rome managed to conquer the northern portions of this peninsula, it struggled to conquer the central and southern parts. This was mainly due to the Macedonian army, which even though only a pale shadow of the great army of Alexander III of Macedon (the Great), was still relatively strong. It took three bloody wars for Rome to finally be able to conquer the rest of the peninsula, and the triumph was mainly because of a mistake of the Macedonian leader.