YOU SAID:

He died whilst mounted apon a steed

INTO JAPANESE

彼は馬に乗ったまま死んだ

BACK INTO ENGLISH

he died on a horse

INTO JAPANESE

彼は馬に乗って死んだ

BACK INTO ENGLISH

He died on a horse.

INTO JAPANESE

彼は馬に乗って死んだ。

BACK INTO ENGLISH

He died on a horse.