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)).
There are two kinds of burial chamber that are refered to as cists or kists. Kist is usually used to refer to a megalithic structure and cist used for later Bronze Age burials.
Cists are small slab lined boxes, set into the ground, with a single slab used as a cover. They tend to be no larger than 1.5m square. Although cists are found in dedicated mounds or cairns they are often later insertions into megalithic cairns (see Kilmashogue (County Dublin)).
Kists are much bigger structures and usually built above ground level (see Dolmen of the Four Maols (County Mayo))and covered by a cairn. They are usually rectangular in plan with vertical sides, but one type, known as a Linkardstown Kist is pentagonal with sloping side stones (see Cloghtogle (County Fermanagh)).