The Carthaginians were Rome's original nemesis. They originally had naval dominance but lost it to Rome in the 1st Punic war. They fielded armies of mercenaries with an emphasis on cavalry. They also had fearsome war elephants, which had a huge shock value on the Romans who had never even seen them before. They were capable of using their cavalry to great effect, as shown in their infamous double envelopment at Cannae which became a textbook maneuver and has influenced military thinking ever since- most notably the German Schlieffen Plan for the western front in the first World War which was planned in the "Cannae Model"