A Piraeus lion is a statue of a lion that was made a long time ago in a place called Piraeus, which is in Greece. It's very special because it's really big and made out of marble, which is a very hard and special kind of rock.
The Piraeus lion is special because it's a little bit different than other statues of lions. Instead of sitting or standing like other lion statues, this lion is laying down on its side. It also has a sort of collar around its neck with a special pattern on it.
People think that the Piraeus lion might have been made to try and show how powerful and strong the people of Piraeus were. They also think that maybe it was made to protect a really important building or street in the city.
The statue is very old and has been around for hundreds and hundreds of years, so it's really special and important to Greek history. Even though it's old, people can still go and look at it now and see how well it has been taken care of over time.