I just started a game with the Parthians last night, and I noticed that they get market buildings and also trade caravans. The caravans are described as causing an "increase in tradable goods." And of course, the Parthians don't get improved roads like the Romans do. I'm wondering if the combination of markets and trade caravans that the Parthians get are equal to or better in terms of trade income than the markets plus roads that the Romans get. If anyone has any insight, please post.