There are two cities called Cartagena; one is in the Bolivar
department of Colombia
and the other is in the autonomous community of Murcia
Cartagena, Spain, is a deep-water port city on the southeast coast of Spain near the eastern side of the Alboran Sea and western limit of the Mediterranean Sea, with a population of about 166,736. The Spanish Navy's Mediterranean squadron is headquartered there; it was the headquarters of the Republican Navy during the Spanish Civil War; and it's also a port of call for the U.S. Navy.
The city was founded by the Carthaginians (hence its name, "Carthago Nova" in Latin) about 225 B.C.; the location was chosen for its silver, lead and iron mines. It continued to flourish under Roman rule after Carthage was destroyed, and even under Moorish rule in the Middle Ages. It was sacked in 1585 by Sir Francis Drake, but recovered and figured in future wars.
Cartagena, Colombia, has the full name of "Cartagena de Indias," and was originally a walled city founded in 1533 as a port for shipping all the riches gathered in the New World back to Spain. It lies on the Caribbean Sea in a fairly defendable location, but was still a target of pirate attacks, so more than a hundred years were spent building up its walls. Its military strength allowed it to resist a British attack in 1741 and gave it the courage to be the first Colombian territory to declare independence from Spain.
The old district is supposed to still look as it did in the early days of the city, but the nearby high-rise district also seems to be a tourist destination and a good place to buy gemstones and coffee. It has a population of about 800,000 and a reputation as a pretty safe place for visitors despite stories of drug-related killings coming from the rest of the country, and a Google search reveals a lot of cruise ships stopping there and also quite a lot of conferences held there.