What do the ancient Spartans mean in the epitaph of Sparta 300?

Epitaphs of 300 Spartan warriors who died heroically in 48 BC;

Go and tell the ancient Spartans, passers-by and passers-by, please tell the Spartans,

We obey their laws and lie here. We are buried here to be loyal to our motherland and people.

Ancient Spartans: Spartans