The Romans called the Mediterranean “Our Sea.” Why do you think this is so?

The Romans referred to it as "their sea" and would not allow competing empires to flourish on it, such as the Greeks and Egyptians. The Mediterranean also connects to other waterways of interest to the Romans such as the Bosporus Straits--this gave the Romans access to the spices and other riches of the East.

Explanation:

The term mare nostrum was used in the first place by Romans to refer to the Tyrrhenian Sea. This was after they had taken over the countries around it. ... So they started to use the name mare nostrum for the whole Mediterranean Sea. They used other names as well, such as Mare Internum ("The Internal Sea").