Their grave's an altar

Simonides of Ceos famously wrote the epigram at Thermopylae marking the self-sacrifice of King Leonidas and his 300 Spartans:

Go tell the Spartans, stranger passing by,
that here obedient to their laws we lie.

Ὦ ξεῖν', ἀγγέλλειν Λακεδαιμονίοις ὅτι τῇδε
κείμεθα, τοῖς κείνων ῥήμασι πειθόμενοι.

From After Thermopylae: The Oath of Plataea and the End of the Graeco-Persian Wars by Paul Cartledge I learn that there was another encomium by Simonides to the Spartans. From Diodorus Siculus, Books 11-12.37.1 by Peter Green.

Of those who died at Thermopylae
Renowned is the fortune, noble the fate:
Their grave's an altar, their memorial our mourning, their fate our praise.

Such a shroud neither decay
Nor all-conquering Time shall destroy.
This sepulcher of brave men has taken the high
Renown of Hellas for its fellow occupant, as witness
Leonidas, Sparta's king who left behind a great
Memorial of valor, everlasting renown.