Situated on the edge of Howth Castle's rhododendron gardens this portal tomb lies a broken, sad monument. The two portal stones still stand ( although one is leaning and may be close to collapse ) and the door slab is still in place, but the huge, rough capstone has slipped, moving the chamber walls and the rear supporting stones.
The capstone measures about 5m x 4m x 1.2m thick and is not finished in any way at all, remaining as rough as the day it broke off the overlooking face of Muck Rock. It must have looked like a giant warty lump when it was in place, in fact it still does.
This is by no means the prettiest of tombs, but the surrounding flowers must make it quite surreal in the early summer.
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)).
Back to one of my favourite places to get some better images and actually measure this monster. These measurements surprised even me. The portal stones are each 2.5 high, 1.5m deep and 70cm thick - this makes them weigh about 7 tonnes each.
The capstone is a massive 5m long, 4.5m broad and 1.8m thick - this means it weighs around 80 tonnes if the uneven thickness is accounted for.
I was also able to study the displaced stones that used to form the chamber before its collapse. These are all similar in size and shape and the three slabs formed a 1.6m cube. What interested me was that it had the same design as the Onagh (County Wicklow) and Larch Hill (County Dublin) tombs.
The portal is aligned southeast.
As I was on Howth again I couldn't resist revisiting this beauty. This time I approached from the south, scrambling over Muck Rock and down into the rhododendron gardens. What a time of year to visit! All the colours!
The paths immediately around the tomb have been improved, but in the trees they are still pretty muddy.
From Dublin city centre take the R105 north and follow the signs to Howth. Carry on along this road until you see the signs for the Transport Museum to the right, this is Howth Castle. Turn in and follow the road past the castle itself until you come to a golf course car park. Park here and walk around the clubhouse on the right-hand side. You will see a footpath entering into the rhododendron gardens. This path splits immediately beyond the hedgerow. Turn right and follow the path for about 100m, looking to your right all the time, ignoring all the rock fall on the left. You will either eventually come to the dolmen or a paved path that leads to it depending on which little route you take.
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.