Mediterranean.
Rome and Carthage are separated by the Mediterranean Sea.
Carthage is not an island, but is near the Mediterranean Sea.
When Carthage and Rome were allies, Carthage was a sea power, Rome a land power. Rome had to organise a fleet when war broke out with Carthage.
Carthage was in moder Tunisia, acoss the sea, to the south of Italy and Rome.
The Mediterranean Sea.
With its warships.
Carthage developed trade and navigation especially by sea. It is not exactly known how far their ships traveled outside the Mediterranean sea because they kept it a strict secret. Carthage was founded around 800 BC by the city of Tyre, and the Carthaginians also founded other cities. Carthage is a common city. Some of examples of Carthage are: Cartage, MO and Carthage, IL.
The Mediterranean Sea.
Carthage in North Africa, and later New Carthage in Spain.
The sea roads of the Mediterranean Sea which separated the two.
There is no river between Rome and Carthage. The two cities are on opposite sides of the Mediterranean Sea.
A powerful Carthage was a threat to Rome's access to the western Mediterranean Sea. Carthage had valuable resources in Spain which Rome wanted access to. Rome also wanted to crush the allies that Carthage had in the Mediterranean Sea area. Her wealth and navy & army could always be a threat to Rome. Thus Rome destroyed Carthage in the Third Punic War.