Binn : Portal Tomb

CountyDonegal
Grid RefC 296 323
Longitude7° 32' 8.98" W
Latitude55° 8' 13.26" N
ITM east480366
ITM north584435
Nearest TownRathmullan (4.8 Km)
OS Sheets2, 3
UTM zone29U
UTM x449041
UTM y5761192
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Visit Notes

Sunday, 5th June 2005

It's odd arriving at a site and being told that you're the first person to visit it in 4 or 5 years. I have had my eye on this site for a while, but only because of my small obsession with visiting every portal tomb .

This one is very ruined. The three slabs forming the 2m x 1m chamber and one of the portal stones is all that remains. It is impossible to get any idea of the site really as it is in a very wooded area with all views obscured by trees. There isn't enough room around the monument to really get a good look at it either.

The tomb is just a few metres into the trees and from the edge of them it is possible to see what's around the site. To the southeast is a low-lying meadow which could once have had a stream running through it. The entrance to the chamber faces east as you would expect in a portal tomb.

Portal tombs are what most people wrongly refer to as dolmens. They are, to me at least, the most strikingly designed of the megalithic tombs. They are called portal tombs because they have two large upright stones, usually very well matched, in front of the chamber that seem to form a doorway.

Resting upon the portal stones and the chamber a large capstone rests (sometimes there are two capstones - see Knockeen (County Waterford)), usually at an angle of around 22 degrees from the horizontal. Although these were originally incorporated into one end of a long cairn there are none left in this state today, although traces of the cairn can sometimes be seen upon the ground. The portal stones can be up to 3.5m tall, which combined with a thick capstone can produce an imposing monument over 5m tall. Capstones can reach in excess of 70 tonnes, with that of Browne's Hill (County Carlow) being estimated at over 120 tonnes.


Often betwen the portal stones there is a door slab, blocking the width of the entrance, but not always the full height. Door slabs are either half height, three quarter height or full height, describing the amount of the portal that they obstruct. All portal tombs would have had door slab, but this has often been removed to facilitate entry into the chamber.

Quite rarely the portal stones are the same height as the chamber and the characteristic slope of the capstone is created by the profile of the capstone (see Glendruid (County Dublin)).

Portal stones are a pair of upright stones that form the 'entrance' to a portal tomb. They are usually well matched, being of even dimensions. As well as forming this doorway they also act as the front support for the capstone and are usually taller than the stones that form the chamber.

Often there is a door stone in between them blocking off access to the chamber within.

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About Coordinates Displayed

This is an explanation of (and a bit of a disclaimer for) the coordinates I provide.

Where a GPS figure is given this is the master for all other coordinates. According to my Garmin these are quite accurate.

Where there is no GPS figure the 6 figure grid reference is master for the others. This may not be very accurate as it could have come from the OS maps and could have been read by eye. Consequently, all other cordinates are going to have inaccuracies.

The calculation of Longitude and Latitude uses an algorithm that is not 100% accurate. The long/lat figures are used as a basis for calculating the UTM & ITM coordinates. Consequently, UTM & ITM coordinates are slightly out.

UTM is a global coordinate system - Universal Transverse Mercator - that is at the core of the GPS system.

ITM is the new coordinate system - Irish Transverse Mercator - that is more accurate and more GPS friendly than the Irish Grid Reference system. This will be used on the next generation of Irish OS maps.

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