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.
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)).
The large rock used to form the roof of a portal tomb or kist.
A compartment in a tomb in which burials were placed. In court tombs and wedge tombs a chamber is a sub-division of the burial gallery. Portal tombs have single chambers and passage tombs can have anything from one to five chambers, although usually passage tombs are considered to have a main chamber with extra subsidary chambers.