# 1911 Encyclopædia Britannica/Vitrified Forts

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​VITRIFIED FORTS, 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.
Since John Williams—one of the earliest of British geologists, and author of The Mineral Kingdom—first described these singular ruins in 1777, about fifty examples have been discovered in Scotland. The most remarkable are Dun Mac Uisneachain (Dun Macsnoichan), the ancient Beregonium, about 9 m. N.N.E. of Oban; Tap o’ Noth, in Aberdeenshire; Craig Phadraic, or Phadrick, near Inverness; Dun Dhardhail (Dunjardil) in Glen Nevis; Knockfarrail, near Strathpeffer; Dun Creich, in Sutherland; Finhaven, near Aberlemno; Barryhill, in Perthshire; Laws, near Dundee; Dun Gall and Burnt Island, in Buteshire; Anwoth, in Kirkcudbright; and Cowdenknowes, in Berwickshire. Dun Mac Uisneachain is the largest in area, being 250 yds. long by 50 yds. broad. In the Tap o’ Noth the walls are about 8 ft. high and between 20 and 30 ft. thick. In Dun Mac Uisneachain, Barryhill and Laws the remains of small rectangular dwellings have been found.
For a long time it was supposed that these forts were peculiar to Scotland; but they are found also in Londonderry and Cavan, in 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; and in several places in France, such as Châteauvieux, Peran, La Courbe, Sainte Suzanne, Puy de Gaudy and Thauron. They have not been found in England or Wales.
In some continental forts the vitrified walls are supported by masses of unvitrified stone built up on each side. This, ​in all probability, constituted an essential feature in the Scottish forts. Except on the hypothesis of buttresses of a similar kind, it is impossible to explain the vast quantities of loose stones which are found both inside and outside many of the vitrified walls.
The method by which the fusion of such extensive fortifications was produced has excited much conjecture. Williams maintained that the builders found out, either during the process of smelting bog ore, or whilst offering sacrifices, the power of fire in vitrifying stone, and that they utilized this method to cement and strengthen their defences. This view has been keenly controverted, and it has been suggested that the vitrified summits were not forts but the craters of extinct volcanoes, an hypothesis long since abandoned; that they are not so much forts as vitrified sites, and that the vitrescence was produced by fires lighted during times of invasion, or in religious celebrations; and, lastly, that if they were forts they must originally have been built of wood and stone, and that their present appearance is due to their being set on fire by a besieging enemy. The theory of Williams has, with modifications, been accepted by the principal authorities. It is supported by the following facts:—
(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, particularly 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) The vitrified walls of the Scottish forts are invariably formed of small stones which could be easily acted upon by fire, whereas the outer ramparts, which are not vitrified, are built of large blocks. (6) 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. (7) Daubrée, in an analysis which he made on vitrified materials taken from four French forts, and which he submitted to the Academy of Paris in February 1881, found the presence of natron in such great abundance that he inferred that sea-salt was used to facilitate fusion. (8) 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.
A great antiquity has been assigned to vitrified forts, without sufficient proof. Articles of bronze and iron have been found in the Scottish forts, while in Puy de Gaudy a Roman tile has been discovered soldered to a piece of vitrified rock. In a few of the German forts Professor Virchow found some of the logs used as fuel in vitrifying the walls, and he concluded from the evenness of their cut surfaces that iron and not stone implements must have been used. These results indicate that these structures were possibly in use as late as the early centuries of the Christian era. It has been suggested that they were built as refuges against the Norsemen. Much in the situation and character of the forts favours this supposition. This is especially the case with reference to the Scottish forts. Here the vitrified summits are invariably so selected that they not only command what were the favourite landing-places of the vikings, but are the best natural defences against attacks made from the direction of the seacoast. In Saxony and Lusatia the forts are known as Schwedenburgen, and in the Highlands of Scotland as the fortresses of the Feinne—designations which also seem to point to an origin dating back to the times of the vikings.
Authorities—John Williams, An Account of some Remarkable Ancient Ruins (1777); A. Fraser Tytler. Edin. Phil. Trans. vol. ii.; Sir George Mackenzie, Observations on Vitrified Forts: Hibbert, Arch. Scot. vol. iv.; J. MacCulloch, Highlands and Western Islands (1824), vol. i.; Hugh Miller, Rambles of a Geologist (1858), chap. ix.; Sir Daniel Wilson, Archaeology and Prehistoric Annals of Scotland (1851), vol. ii.; J. H. Burton, History of Scotland (1867), vol. i.; R. Angus Smith, Loch Etive and the Sons of Uisneach (1879); J. Anderson, Scotland in Pagan Times (1886); C. MacLagan, The Hill Forts of Ancient Scotland; Thomas Aitken, Trans. Inverness Scientific Soc. vol. i.; Charles Proctor, Chemical Analysis of Vitrified Stones from Tap o' Noth and Dunideer (Huntly Field Club); various papers in Proceedings of Soc. Antiq. Scot. (since 1903 The Scottish Historical Review) and Proceedings of Royal Irish Academy; R. Munro, Prehistoric Scotland (1899); G. Chalmers, Caledonia (new ed., 7 vols., Paisley, 1887–94); Murray's Handbook to Scotland (1903 ed.); Leonhard, Archiv für Mineralogie, vol. i.; Virchow, Ztschr. für Ethnologie, vols. iii. and iv.; Schaaffhausen, Verhandlungen der deutsch. anthrop. Gesellschaft (1881); Köhl, Verhand. d. deutsch. anthrop. Gesellschaft (1883); Thuot, La Forteresse vitrifiée du Puy de Gaudy, &c.; De Nadaillac, Les Premiers Hommes, vol. i.; Mémoires de la Soc. Antiq. de France, vol. xxxviii.; Hildebrand, De forhistoriska folken i Europa (Stockholm, 1880); Behla, Die vorgeschichtlichen Rundwälle im östlichen Deutschland (Berlin, 1888); Oppermann and Schuchhardt, Atlas vorgeschichtlicher Befestigungen in Niedersachen (Hanover, 1888-98); Zschiesche, Die vorgeschichtlichen Burgen und Wälle im Thüringer Zentralbecken (Halle, 1889); Bug, Schlesische Heidenschanzen (Grottkau, 1890); Gohausen, Die Befestigungsweisen der Vorzeit und des Mittelalters (Wiesbaden, 1898).  (R. Mu.*)