Wine was transported in bulk in antiquity in a variety of ways: in huge wineskins loaded on the backs of two- or four-wheeled carts or in barrels on carts, but water-borne transport had a great advantage because of the inefficiency of the harnesses used on animals. For most of the Mediterranean area, wine was carried in large amphorae, which were loaded in the holds of ships. The pottery jars required considerable packing (heather, straw, etc.) to cushion them against breakages. They could be transferred to smaller vessels for transport up inland waterways. A recent discovery has been of wrecks carrying dolia, as a kind of tanker for the bulk transport of wine. Barrels were widely used in northern Europe (see celts) and later in the Mediterranean, although the amphora tradition died out completely only in the medieval period.