They expanded from direct trade - exchanging goods, to carriage
trade where the multiplied their trading by carrying goods between
other regions. This trade covered foodstuffs, wines, timber,
minerals, precious items, fabrics, other manufactured goods and
artwork.
They exchanged them for other tradeable goods such as metals
metal ores, foodstuffs, pottery, materials. When coinage became
common later on, it could be used as a medium of exchange.