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Ordnance Survey Benchmark

Ref: BM080

This benchmark is located along the parapet wall in the Moorish Castle Estate, above the Northern Defences in the Upper Town area.

It is chiselled directly into the limestone stone wall and bears its BM number 243.046 in addition to the broad arrow symbol.

It features on the 1866 OS Survey Map of Gibraltar (updated up to the 1940’s).

 

Ordnance Survey Benchmarks

The broad arrow symbol topped with a horizontal line can be seen chiselled on masonry in locations throughout Gibraltar denoting Ordnance Survey benchmarks which first appeared in the OS map of Gibraltar carried out in 1865 by the Royal Engineers. The Royal Engineers used these benchmarks to calculate each position relative to the heights of nearby benchmarks in a network extending from a fundamental benchmark which was a point with a precisely known relationship to the vertical datum of the area, typically mean sea level. A number of benchmarks can still be seen on the base of the Line Wall which marked the extent of the land mass just above sea-level. The location and height of each benchmark was then shown in the army OS maps right up to the 1930’s.

Demolition of many old buildings, road enlargements and the return of dense vegetation to many parts of the Upper Rock has destroyed or obscured many of these benchmarks, but many marks remain extant to this day.

Ordnance Survey Benchmark Image

MAP LOCATION