The Sentry Box is a Grade II* listed building in the Cornwall local planning authority area, England. First listed on 9 October 1987. A Medieval Defensive structure.

The Sentry Box

WRENN ID
peeling-facade-acorn
Grade
II*
Local Planning Authority
Cornwall
Constituency
St Ives MP: Andrew George (LD)
Country
England
Date first listed
9 October 1987
Type
Defensive structure
Period
Medieval
Address
The Sentry Box, St. Michael's Mount
OS grid reference
SW 514 298
Coordinates
50.11682, -5.47855
Source
Historic England listing

Also on this page: flood risk · radon risk · weather exposure · detailed attributes ↓

Description

The Sentry Box is a defensive wall dating from the 15th century, located on St Michael's Mount in Marazion. It is constructed from battered granite rubble and built over a rocky outcrop. The wall features a thick retaining structure with a sentry box at its northern end and a gateway at its southern end. There are three embrasures that are splayed on both sides of the wall. The sentry box is small, just large enough for a person to stand inside, and is roofed with corbelled granite slabs that slope down to a ridge slab. It has small lookout openings on three outer sides and a doorway on the inner (west) side. The rocky outcrop within the structure was formerly known as St Michael's Chair, which was later relocated to the church tower.

Local climate

The Sentry Box receives an average of 910 mm of rain a year. This makes it wetter than 68% of listed buildings in the UK. Its exposure to wind-driven rain is greater than that of 91% of listed buildings.

It experiences an average of 4 freeze-thaw cycles a year, fewer than 98% of listed buildings. Of these, 1 follows at least 1 mm of rain in the preceding 48 hours. Average temperatures at this location have risen by 0.3°C per decade since 1991.

Averages for 1991–2020; temperature trend 1991–2025. Figures describe the wider area (a grid cell of roughly 10 km), not the individual site. Contains modified Copernicus Climate Change Service information 2026.

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Nearby listed buildings

  1. The French Gun Battery (North West Corner) Grade II* 20 m
  2. Gun Battery North-North West of St Michael's Mount Qv. Grade II* 34 m
  3. The Church of Saint Michael Grade I 45 m
  4. St Michael's Mount Grade I 54 m
  5. Cross Shaft West of St Michael's Mount Grade II 55 m
  6. Gun Battery West of St Michael's Mount Qv. Grade II* 65 m
  7. Pinnacle on Shaft Grade II 66 m
  8. Cross North East of St Michael's Mount Grade II 68 m
  9. Cross Near South East Corner of St Michael's Mount Grade II* 68 m
  10. Well Beside Path Leading to St Michael's Mount Grade II 88 m