Behold, they were dead

The word "behold" is used here to mark a surprising event.

they were dead, fallen to the ground

The phrase "fallen to the ground" is an idiomatic way to say that "they were dead." Alternate translation: "they were all dead on the ground" (See: rc://en/ta/man/translate/figs-idiom and rc://en/ta/man/translate/figs-doublet)