The great sweet wine of antiquity, made from grapes dried to raisins before pressing so the sugar concentrates — a technique, not a single recipe. Carthaginian in origin (the only surviving fragment of Mago's farming manual, preserved by Columella, describes it), passum was made across the Roman world and prized as a luxury, a wine for feasts.
Of all ancient wines this is the one with living heirs. The method passes in an unbroken conceptual line to the straw wines and passiti of today — vin de paille, Recioto, Vin Santo, Commandaria — all of them raisining grapes as passum did. What continues is the idea; the specific ancient wine, like the rest, is gone.