Vitrified fort

Weak parts of the defence are strengthened by double or triple walls, and occasionally vast lines of ramparts, composed of large blocks of unhewn and unvitrified stones, envelop the vitrified centre at some distance from it.

In some cases the stones are only partially melted and calcined; in others their adjoining edges are fused so that they are firmly cemented together; in many instances pieces of rock are enveloped in a glassy enamel-like coating which binds them into a uniform whole; and at times, though rarely, the entire length of the wall presents one solid mass of vitreous substance.

[4][5] The expert consensus explains vitrified forts as the product of deliberate destruction either following the capture of the site by an enemy force or by the occupants at the end of its active life as an act of ritual closure.

[6] Since John Williams, one of the earliest of British geologists, and author of The Natural History of the Mineral Kingdom, first described these singular ruins in 1777, over 70 examples have been discovered in Scotland.

[2] The most remarkable are: For a long time it was supposed that these forts were peculiar to Scotland; but they are found also in the Isle of Man (Cronk Sumark); County Londonderry and County Cavan, Ireland; in Upper Lusatia, Bohemia, Silesia, Saxony, and Thuringia; in the provinces on the Rhine, especially in the neighbourhood of the Nahe; in the Ucker Lake; in Brandenburg, where the walls are formed of burnt and smelted bricks; in Hungary; in several places in France, such as Châteauvieux (near Pionnat), Péran, La Courbe, Sainte-Suzanne, Puy de Gaudy, and Thauron; also rarely in the north of England.