“It takes place in Ancient Rome.”
There's a TV show that you like which is about Roman gladiators. You're describing the show to a friend who hasn't seen it. You start by saying this.
It takes place in Ancient Rome.
Use this phrase to describe the setting of a movie, book, TV show, play, etc. The phrasal verb "take place" means to "happen", so the sentence describes where and when the story happens.
You can follow "take place" with either a time, a location, or both:
It takes place in the 1930's.
The novel takes place in rural China.
I saw a movie that took place in 18th century France.
It takes place in a school for young wizards and witches.
Another way to explain the same idea is "___ is set in ___":
It's set in Ancient Rome.
The word "ancient" means "extremely old". One way that people use it is to name famous civilizations in history. Some of the most common examples are:
All of these civilizations are more than a thousand years old.