On a map, a border is a solid black line. On the ground, it can feel like a fiction. I'm standing on the edge of a shallow stream through the forest that separates two West African countries: Ivory Coast and Liberia. Here there is no fence. No sign. No border guard to prevent my crossing.
On either side of this stream, people speak the same local language, Yokuba, a language incomprehensible to most of their countrymen. They share the same currency, the West African CFA franc, as well as a currency of trust built up over generations of intermarriage and communal life.