Joseph wrote that he translated the BOM from hieroglyphs.
Times and Seasons 4, no. 24 (November 1, 1843): 373
The fact is, that by the power of God I translated the Book of Mormon from hieroglyphics; the knowledge of which was lost to the world: in which wonderful event I stood alone, an unlearned youth, to combat the worldly wisdom, and multiplied ignorance of eighteen centuries