The comprehensive gazetteer and bibliography of the medieval castles, fortifications and palaces of England, Wales, the Islands.
The listings
Other Info
Print Page 
Next Record 
Previous Record 
Back to list 

Harrys Walls

Also known as, or recorded in historical documents as;
Mount Flagon

In the civil parish of St Marys.
In the historic county of Isles of Scilly.
Modern Authority of Isles of Scilly.
1974 county of Isles of Scilly.
Medieval County of Isles of Scilly.

OS Map Grid Reference: SV90951089
Latitude 49.91836° Longitude -6.30674°

Harrys Walls has been described as a certain Artillery Fort.

There are masonry ruins/remnants remains.

This site is a scheduled monument protected by law.


Harry's Walls comprise of an unfinished artillery castle dating to the mid-16th century, situated on the summit of Mount Flagon, overlooking St Mary's Pool. It was begun in 1551 as part of a major phase of fortification on the Isles of Scilly, undertaken between 1547 and 1554, to counter threats from the French. By 1554, some of the garrison was transferred to Tresco, reflecting a shift in the focus of fortification. This artillery castle would have been the first fortification in the country to have been provided entirely with angled bastions and straight orillions, a design at the forefront of military engineering. However it was never completed since the site was not entirely suitable. The crown of Mount Flagon was too small to accommodate a castle of this size and the location was strategically poor, unable to fully cover the approaches to the anchorage. On the south west side of the monument is a massive stone curtain wall terminating in a pointed bastion at each end, facing west and south. On the north west side is an unfinished rock-cut ditch. The curtain wall is faced on each side by granite blocks and is infilled with granite rubble. The bastion walls, either side of the curtain wall, are defined by massive acutely angled walls pointing directing away from the corner of the castle. They average 21 metres long and 5 metres wide and rise up to 2.3 metres high externally. The angled outer walls of each bastion are joined to the ends of the curtain wall by a short linking wall. These were designed to mount guns that would provide flanking fire along the outside of the curtain walls. Within each bastion is a small sub-triangular internal area linked to the castle interior by a narrow entry passage through the walls. Work on the castle was abandoned before the curtain walls facing north west, north east and south east, or the north and east bastions were constructed. (PastScape)
Links to archaeological and architectural databases, mapping and other online resources

Data >
PastScape   County HER   Scheduling        
Maps >
Streetmap   NLS maps   Where's the path   Old-Maps      
Data/Maps > 
Magic   V. O. B.   Geology   LiDAR   Open Domesday  
Air Photos > 
Bing Maps   Google Maps   Getmapping   ZoomEarth      
Photos >
CastleFacts   Geograph   Flickr   Panoramio      

Sources of information, references and further reading
Most of the sites or buildings recorded in this web site are NOT open to the public and permission to visit a site must always be sought from the landowner or tenant.
It is an offence to disturb a Scheduled Monument without consent. It is a destruction of everyone's heritage to remove archaeological evidence from ANY site without proper recording and reporting.
Don't use metal detectors on historic sites without authorisation.
The information on this web page may be derived from information compiled by and/or copyright of Historic England, County Historic Environment Records and other individuals and organisations. It may also contain information licensed under the Open Government Licence. All the sources given should be consulted to identify the original copyright holder and permission obtained from them before use of the information on this site for commercial purposes.
The author and compiler of Gatehouse does not receive any income from the site and funds it himself. The information within this site is provided freely for educational purposes only.
The bibliography owes much to various bibliographies produced by John Kenyon for the Council for British Archaeology, the Castle Studies Group and others.
Suggestions for finding online and/or hard copies of bibliographical sources can be seen at this link.
Minor archaeological investigations, such as watching brief reports, and some other 'grey' literature is most likely to be held by H.E.R.s but is often poorly referenced and is unlikely to be recorded here, or elsewhere, but some suggestions can be found here.
The possible site or monument is represented on maps as a point location. This is a guide only. It should be noted that OS grid references defines an area, not a point location. In practice this means the actual center of the site or monument may often, but not always, be to the North East of the point shown. Locations derived from OS grid references and from latitude longitiude may differ by a small distance.
Further information on mapping and location can be seen at this link.
Please help to make this as useful a resource as possible by contacting Gatehouse if you see errors, can add information or have suggestions for improvements in functality and design.
Help is acknowledged.
This record last updated 26/07/2017 09:22:45

Home | Books | Links | Fortifications and Castles | Other Information | Help | Downloads | Author Information | Contact