A made way across a gap that would otherwise stop passage. A bridge belongs to neither side and serves both.
Old English brycg (bridge), from Proto-Germanic *brugjō, from a Proto-Indo-European root *bhrū- (log, beam, wooden causeway). Cognate with German Brücke. The oldest sense is not the arch but the LAID BEAM — a tree felled across a gap, which is the first bridge anyone made.
The switchboard: the knowledge delivery system where the seven Lines hold every ward in code. The felled-log sense is the honest one — a bridge is a deliberate thing placed across a gap that would otherwise stop you, and someone has to maintain it.