The exchange of material goods facilitates inter-ethnic contact and stimulates culture change but in the past such interactions have tended to be concentrated within certain regions separated by natural barriers from other regions of the world. However, for many centuries there has been some long-distance exchange not only of material goods but also ideas, values and skills which are less obvious when trying to interpret visible, material remains from the past. Nowadays the process of cross-cultural interaction has speeded up, so the whole world is becoming a huge ‘Mega-culture’.