Gurteen Rath is situated about four miles from Mullingar. Within it is an interesting souterrain, of which the accompanying figure is a plan. The entrance is on the east side, and the passage is 17 feet long, 3 feet wide, and 3 feet high. At the end a step of 10 inches, and at the same time an additional rise in the height, give an elevation to the roof of about 6 feet; to the right is another passage leading to a circular chamber 7 feet high. The main passage takes a curve to the west, and at 12 feet a short passage leads to another circular, but smaller, chamber. Continuing, and making a full distance of 46 feet, the main passage ends in a third, and largest, circular chamber, 7½ feet high and 10½ in diameter. The chambers are of the ordinary bee-hive pattern.[80] [Illustration: Plan of Souterrain, Gurteen Rath, near Mullingar.] The date of the Irish souterrains is as difficult to determine as that of the raths themselves. From their similarity to the sepulchral chambers it has been thought by some that they were constructed by the same race of people and about the same time. But there are essential points of difference between them: souterrains are generally much more complicated in plan, and were evidently designed to be defended; they are underground, whereas the sepulchral chambers are under raised mounds; the latter are megalithic, while, as a rule, the former are microlithic, although in the case of the Doon souterrain, stones 9 and 10 feet in length were used.[81] The presence of Ogam stones in some, as has already been mentioned, would point to a period for their construction subsequent to the use of these stones as monuments. Whatever the date of the construction of these places of security may have been, there can be very little doubt of the necessity for their use at least in early mediæval times. When we take into account the lawlessness, and the insecurity and indifference to human life during the Norse period of invasion, which, as the Annalists fully testify, were only too common under the rule of irresponsible petty kings and chiefs, we can readily understand the necessity of refuges such as the forts and underground chambers afforded, by which the construction of some may perhaps be accounted for. * * * * *