One of the oldest and most widespread social institutions is the exchange of goods, or trade. Most ancient trade consisted of barter, where two traders would exchange goods with one another. The widespread practice of trade allowed civilizations to exchange raw materials and goods which they had in abundance or could easily produce, for items that were rare or nonexistent in their geographic region. The introduction of regulated currency that could be exchanged for items resulted in easier, more convenient trade. Merchants soon roamed the world, connecting different lands with webs of economic interdependence. In addition to goods and profits, traders also brought back tales and technology from these foreign lands. Well-traveled traders like Marco Polo were among the most learned sources on the cultures and traditions of foreign lands.