…the Messenians, who have entrenched themselves at…

…the Messenians, who have entrenched themselves at Mount Ithome and successfully resist Spartan efforts to dislodge them. (Ithome, together with the Acrocorinth, the citadel of Corinth, was described by a Hellenistic ruler as one of the “horns of the Peloponnesian ox” that a would-be conqueror must seize.)

Possibly, the occupiers of Ithome plan not only an act of secession but, in fact, an attack on the famously unravaged city of Sparta itself.

The earthquake not only shakes Spartan nerve but must also have serious demographic effects (though how long-term these are is disputed).