πεντηκοστῷ ἔτει—if the number is exact, the previous eruption would be in 475 or 474 B.C. There is a magnificent description of an eruption of Etna in Pindar's first Pythian (474 B.C.), and in Aeschylus, Prometheus Vinctus (circa 468 B.C.). An eruption is recorded as occurring at the time of the battle of Plataea, 479 B.C.
λέγεται shows that Thuc. was not quite sure as to the exact date.
τρὶς γεγενῆσθαι—the ‘first’ eruption is legendary. A fourth is recorded in 396 B.C.
