Cartagena is a city located in the southeast of Spain, near the Mediterranean Sea. It's a very old and historic city that has been around for a long time, even before the Romans came to Spain.
Imagine you have a big box of toys and you put all your favorite toys in one corner of the box. That's kind of like what happened in Cartagena - people wanted to settle in one corner of the city because it had a natural harbor and was easy to trade with other places.
Over time, different groups of people came and went from Cartagena. The Romans were one of the most important groups, and they built a lot of things that are still standing in the city today. One of those things is an amphitheater, which is like a big outdoor stadium where people would watch shows and battles.
After the Romans left, Cartagena became part of different kingdoms and empires, and it changed a lot over the years. But one thing that has always been important here is the sea. Even today, Cartagena is a really busy port, where ships come and go with all kinds of things from all over the world.
Overall, Cartagena is a really interesting place with a long and rich history. It's a great place to visit if you want to learn more about Spain and see some ancient ruins and beautiful scenery.