From Old English (before 12th century), from Proto-Indo-European '*kreuk-' ("back, spine"), from PIE *kreuk- ("back, spine").
A long narrow hilltop, mountain range, or watershed; the line formed where two sloping surfaces meet at the top.
From Old English 'hrycg' (spine, back of a person or animal; ridge, elevated ground), from Proto-Germanic '*hrugjaz' (back, spine, ridge), from PIE root *kreuk- (back, spine, ridge). The word originally meant the spine or back of an animal — ridges of land were seen as the Earth's backbone. The same sense-development occurred independently in many languages
The Ridgeway in England — one of the oldest roads in Europe, used continuously for 5,000 years — gets its name from Old English 'hrycg-weg' (spine-road), because it follows the chalk ridge of the Berkshire Downs. Travelers preferred ridge roads because they stayed dry above the muddy valleys, and you could see enemies coming from miles away.