Okay kiddo, have you ever heard of Alexander the Great? He was a very famous king who lived a long, long time ago. He ruled a big empire that included a lot of places in Europe and Asia. Well, one of the most interesting things that people talk about when they talk about Alexander is something called the Gates of Alexander.
Now, the Gates of Alexander were not actual gates like you might see at a park, or a museum. They were more like a metaphor, which is a way of talking about something without actually using the thing itself. So, the Gates of Alexander were like a big, big wall that separated what Alexander considered to be the civilized world from the rest of the world, which he thought of as wild and barbaric.
Alexander thought that if he could find these gates, he could conquer the whole world, because he thought that the place beyond the gates would be full of treasures, riches and amazing things. People think that he might have been talking about mountains or valleys, but no one is really sure.
In any case, the idea of the Gates of Alexander became a really popular story, and people still talk about it today. Some people even believe that they have found the Gates and that they lead to a secret treasure! But, like with a lot of things, it's hard to say for sure.
So, in short, the Gates of Alexander were an imaginary wall that separated the civilized and wild world, and people still talk about them because they are really interesting!