Center and Edge

I read once that a difference between the first Europeans who came here and the indigenous people they found was their sense for the role of rivers.  For the newcomers, a river marked a boundary. "My land is on this side, yours on the other."  For the native peoples, the river was the center of a territory, the surrounding mountains forming borders.  This seems more wholistic, a homeland and a watershed as one and the same.  Is the river the center of a place?  Is it at the edge? 

I find it striking that the river both unites and divides.  It pulls water down from its root-shaped system of feeder streams, gathering an ever-expanding flow.  At the same time, it creates a barrier, a border, a place where you have to find a bridge.