Vitrified Forts

Vitrified Forts, such as that at Knockfarrel above Strathpeffer, are the name given to certain rude stone enclosures whose walls have been subjected in a greater or less degree to the action of fire. They are generally situated on hills offering strong defensive positions. Their form seems to have been determined by the contour of the flat summits which they enclose. The walls vary in size, a few being upwards of 12 ft. high, and are so broad that they present the appearance of embankments.

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. No lime or cement has been found in any of these structures, all of them presenting the peculiarity of being more or less consolidated by the fusion of the rocks of which they are built. This fusion, which has been caused by the application of intense heat, is not equally complete in the various forts, or even in the walls of the same fort. 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.

Knockfarrel is a conical hill topped by a vitrified fort in Easter Ross in Highland Council Area, Knockfarrel rises to 190 m (579 feet) to the east of Strathpeffer. It forms the summit of a ridge called Druim Chat (Cat's Back).

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