The most remarkable of these forts may still be seen in the Isles of Arran, on the west coast of Galway; there are others in Donegal, Mayo, and in Kerry.

Some of these erections have chambers in their massive walls, and in others stairs are found round the interior of the wall; these lead to narrow platforms, varying from eight to forty-three feet in length, on which the warriors or defenders stood.

The fort of Dunmohr, in the middle island of Arran, is supposed to be at least 2,000 years old.

Besides these forts, there was the private house, a stone habitation, called a _clochann_, in which an individual or family resided; the large circular dome-roofed buildings, in which probably a community lived; and the rath, intrenched and stockaded.
But stone was not the only material used for places of defence or domestic dwellings; the most curious and interesting of ancient Irish habitations is the _crannoge_, a name whose precise etymology is uncertain, though there is little doubt that it refers in some way to the peculiar nature of the structure.
The crannoges were formed on small islets or shallows of clay or marl in the centre of a lake, which were probably dry in summer, but submerged in winter.

These little islands, or mounds, were used as a foundation for this singular habitation.