Monument at North Western End of General Roys Survey Base
MONUMENT AT NORTH WESTERN END OF GENERAL ROYS SURVEY BASE, NORTHERN PERIMETER ROAD
Listed on the National Heritage List for England. Search over 400,000 listed places
Overview
- Heritage Category:
- Listed Building
- Grade:
- II
- List Entry Number:
- 1119717
- Date first listed:
- 15-Dec-1997
- List Entry Name:
- Monument at North Western End of General Roys Survey Base
- Statutory Address:
- MONUMENT AT NORTH WESTERN END OF GENERAL ROYS SURVEY BASE, NORTHERN PERIMETER ROAD
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Location
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Images of England Project
- Date:
- 2007-05-02
- Reference:
- IOE01/16466/27
- Rights:
- © Mr Anthony Rau. Source: Historic England Archive
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Discover moreOfficial list entry
- Heritage Category:
- Listed Building
- Grade:
- II
- List Entry Number:
- 1119717
- Date first listed:
- 15-Dec-1997
- List Entry Name:
- Monument at North Western End of General Roys Survey Base
- Statutory Address 1:
- MONUMENT AT NORTH WESTERN END OF GENERAL ROYS SURVEY BASE, NORTHERN PERIMETER ROAD
The scope of legal protection for listed buildings
This List entry helps identify the building designated at this address for its special architectural or historic interest.
Unless the List entry states otherwise, it includes both the structure itself and any object or structure fixed to it (whether inside or outside) as well as any object or structure within the curtilage of the building.
For these purposes, to be included within the curtilage of the building, the object or structure must have formed part of the land since before 1st July 1948.
The scope of legal protection for listed buildings
This List entry helps identify the building designated at this address for its special architectural or historic interest.
Unless the List entry states otherwise, it includes both the structure itself and any object or structure fixed to it (whether inside or outside) as well as any object or structure within the curtilage of the building.
For these purposes, to be included within the curtilage of the building, the object or structure must have formed part of the land since before 1st July 1948.
Location
- Statutory Address:
- MONUMENT AT NORTH WESTERN END OF GENERAL ROYS SURVEY BASE, NORTHERN PERIMETER ROAD
The building or site itself may lie within the boundary of more than one authority.
- County:
- Greater London Authority
- District:
- Hillingdon (London Borough)
- Parish:
- Non Civil Parish
- National Grid Reference:
- TQ0771476789
Details
TQ 07 NE
804/47/10049
NORTHERN PERIMETER ROAD
Heathrow Airport
Monument at north-western end of General Roy's survey base
II
Cast-iron cannon monument, installed 1791 to mark the north-western end of the baseline measured by General Roy in 1784 across Hounslow Heath, from King's Arbour to Hampton Poor House, which is now taken to be the origin of the Ordnance Survey. Roy originally marked his line by wooden posts, but in 1791 two guns were selected at Greenwich 'from amongst those which had been condemned as unfit for the public service'. The cannon is some nine feet long, the lower six feet of which are buried in the ground. Next to the cannon is a plaque which reads as follows:
'This tablet was affixed in 1926 to commemorate the 200th anniversary of the birth of Major General William Roy FRS, born 4th May 1726 - died 1st July 1790. He conceived the idea of carrying out the triangulation of this country and of constructing a complete and accurate map and thereby laid the foundation of the Ordnance Survey. This gun marks the NW terminal of the base which was measured in 1784, under the supervision of General Roy, as part of the operations for determining the relative positions of the Greenwich and Paris Observatories. This measurement was rendered possible by the munificence of HM King George III, who inspected the work on 21st August 1784. The base was measured again in 1791, by Captain Mudge, as the commencement of the principal triangulation of Great Britain. Length of base - reduced to MGL - as measured by Roy - 27404.01 feet, as measured by Mudge - 27404.24 feet, as determined by Clarke in 1858 in terms of the Ordnance Survey Standard 01 - 27406.19 feet.'
Source: Captain William Mudge and Isaac Dalby, An Account of the Operations Carried on for Accomplishing a Trigonometric Survey of England and Wales, vol. 1, 1799, p.223.
The monument at the south-east end of General Roy's baseline is listed under Roy Grove, Hampton, in the London Borough of Richmond.
Listing NGR: TQ0771476789
Legacy
The contents of this record have been generated from a legacy data system.
- Legacy System number:
- 469215
- Legacy System:
- LBS
Sources
Books and journals
Mudge, , Dalby, , An Account of the Operations Carried on for Accomplishing a Trigonometric Survey of England and Wales Volume I, (1799), 223
Legal
This building is listed under the Planning (Listed Buildings and Conservation Areas) Act 1990 as amended for its special architectural or historic interest.
Map
This map is for quick reference purposes only and may not be to scale. This copy shows the entry on 02-Jul-2026 at 09:16:35.
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