VITRIFIED FORTS, the name given to certain hill-forts of which the defences consist entirely or to some extent of walls which have been subjected in a greater or less degree to the action of fire. Their form is determined by the contour of the summits which they enclose and generally the plan is simple. The walls vary in size, the vitrified portion being usually confined to a core extending from the top downwards, though vitrifaction has been met with on the sides of the wall only, and in one known instance a narrow wall consolidated by vitrifaction was found in the heart of an earthen rampart. As a rule the vitrified mass appears to have been supported by a wall of unvitrified stone built up on one or both faces. No lime or cement has been found in any of these structures, all of them presenting the peculiarity of being consoli dated to a greater or less extent by the fusion of the rocks of which they are built. This fusion, caused by the application of in tense 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 in stances 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.
Some so examples have been discovered in Scotland widely dis tributed. They are also found in Ireland, 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 ; and in several places in France. They have not been found in England or Wales.
The following facts may be noted :—(1) The idea of strengthening walls by means of fire is not singular, or confined to a distinct race or area, as is proved by the burnt-earth enclosure of Aztalan, in Wisconsin, and the vitrified stone monuments of the Mississippi valley. (2) Many of the Primary rocks, particu larly the schists, gneisses and traps, which contain large quantities of potash and soda, can be readily fused in the open air by means of wood fires—the alkali of the wood serving in some measure as a flux. (3) The walls are chiefly vitrified at the weakest points,
the naturally inaccessible parts being unvitrified. (4) When the forts have been placed on materials practically infusible, as on the quartzose conglomerates of the old red sandstone, as at Craig Phadraic, and on the limestones of Dun Mac Uisneachain, pieces of fusible rocks have been selected and carried to the top from a considerable distance. (5) Many of the continental forts are so constructed that the fire must have been applied internally, and at the time when the structure was being erected. (6) Daubree, in an analysis of vitrified materials taken from four Fren forts, which he submitted to the Academy of Paris in Feb. 1881, found the presence of natron in such abundance that he inferred that sea-salt was used to facilitate fusion. (7) In Scandinavia, where there are hundreds of ordinary forts, and where for centuries a system of signal fires was enforced by law, no trace of vitrifaction has yet been detected.
Williams, An Account of some Remarkable Ancient Ruins (1777) ; J. Anderson, Scotland in Pagan Times (1886) ; Christison, Early Fortifications in Scotland; Proceedings of Soc. Antiq. Scot. vols. viii., xxxix., xl., xlviii. ; the inventories of the Royal Corn mission on the Ancient and Historical Monuments of Scotland; Proceedings of Royal Irish Academy; R. Munro, Prehistoric Scotland (1899) ; Leonhard, Archiv fur Mineralogie, vol. i. ; Virchow, Ztschr. fiir Ethnologie, vols. iii. and iv.; Schaaffhausen, Verhandlungen der deutsch. anthrop. Gesellschaft (1881) ; Kohl, Verhand. d. deutsch. anthrop. Gesellschaft (1883) ; Thuot, La Forteresse vitrifiee du Puy de Gaudy, etc.; De Nadaillac, Les Premiers Hommes, vol. i.; Memoires de la Soc. Antiq. de France, vol. xxxviii. ; Hildebrand, De forhistoriska folken i Europa (Stockholm, 188o) ; Behla, Die vorge schichtlichen Rundwalle im ostlichen Deutschland (Berlin, 1888) ; Oppermann and Schuchhardt, Atlas vorgeschichtlicher Befestigungen in Niedersachen (Hanover, 1888-98) ; Zschiesche, Die vorgeschicht lichen Burgen and Wane im Thiiringer Zentralbecken (Halle, 1889) ; Bug, Schlesische Heidenschanzen (Grottkau, 189o) ; Gohausen, Die Befestigungsweisen der Vorzeit und des Mittelalters (Wiesbaden, 1898) ; Transactions of the Buteshire Natural History Society (1914 z5 and 1925).