There are two man-made cairns on the summit.
Brown Willy Summit Cairn or Brown Willy North Cairn is a man made rock pile that sits alongside an Ordnance Survey triangulation station.

The Cornish word for "cairn" is karn (from karnow, meaning "rock piles"), and it has been suggested that Cornwall's ancient name  Kernow is related.
 William Copeland Borlase classified ridge-top cairns such as these in the most common category a "bowl"- or "cone"-shaped tumulus.
He also referred to them as "sepulchral mounds" but admitted that burials had not been found at many.
Brown Willy Summit Cairn has never been excavated and folklore suggests an ancient Cornish king may lie entombed underneath.
Nicholas Johnson and Peter Rose dated nine of the cairns on Bodmin Moor, eight gave mean date ranges between 2162 and 1746 cal BC, suggesting the early Bronze Age was the main building period for cairns of this type.
These are amongst the most intact due to their remote and inaccessible location.
Many rocks from similar cairns have been spoiled and removed over centuries of neglect to be re-used in dry stone walling and other local construction.

Rodney Castleton has suggested that from the centre of Stannon stone circle, the autumn equinox sun rises over Brown Willy North Cairn.
and Christopher Tilley refers to a "dramatic association with Rough Tor.
These purported alignments have been taken as evidence of some astronomical purpose in cairn placement and construction.
There are two man-made cairns on the summit. Brown Willy Summit Cairn or Brown Willy North Cairn is a man made rock pile that sits alongside an Ordnance Survey triangulation station.
The Cornish word for "cairn" is karn (from karnow, meaning "rock piles"), and it has been suggested that Cornwall's ancient name  Kernow is related.  William Copeland Borlase classified ridge-top cairns such as these in the most common category a "bowl"- or "cone"-shaped tumulus. He also referred to them as "sepulchral mounds" but admitted that burials had not been found at many. Brown Willy Summit Cairn has never been excavated and folklore suggests an ancient Cornish king may lie entombed underneath. Nicholas Johnson and Peter Rose dated nine of the cairns on Bodmin Moor, eight gave mean date ranges between 2162 and 1746 cal BC, suggesting the early Bronze Age was the main building period for cairns of this type. These are amongst the most intact due to their remote and inaccessible location. Many rocks from similar cairns have been spoiled and removed over centuries of neglect to be re-used in dry stone walling and other local construction.
Rodney Castleton has suggested that from the centre of Stannon stone circle, the autumn equinox sun rises over Brown Willy North Cairn. and Christopher Tilley refers to a "dramatic association with Rough Tor. These purported alignments have been taken as evidence of some astronomical purpose in cairn placement and construction.
Brown Willy