Classification of Vitrified Forts

Exploration of vitrified fort classification

Currently, there is a single grouping of vitrified forts, it is our contention that in reality only a few forts should be classified as such, and that analysis would be helped if this classification was further refined. In order to perform better asnalysis of vitrified forts, it will be neccesary to attempt to classify the various features, the following discussion examines some possible options.

General Classification

1. Partially Vitrified or burnt forts where isolated areas of the fort are affected.
2. Totally Vitrified forts which have large areas of even vitrification..

Partial vitrification can occur where an intense heat causes vitrifaction in one or more isolated locations along part of the rampart, or where the temperatures were never so high as to cause the rock to melt. Such forts could include  Almondbury in Yorkshire where the excavation evidence indicates the fire started from a small area and the heat involved may not have been as high as 600 C. The causes of such vitrification and burning could be the result of attack or from accidental fire damage due to gateways or buildings burning in a prolonged and uncontrolled manner. In these cases it is probable that relatively small areas of burnt stone may occur, however it is our conjecture that since the design of the rampart meant fire would spread only with difficulty and would be easily doused by the inhabitants of the fort.

that ese types of forts from forts which are Totally Vitrified. Also included in this classification are forts which have been burnt as a result of a battle, the reason for this is that the intense heat required to cause the sorts of vitrification observed could only be the result of careful planning, it is not likely that enough fuel would have been easily to hand.

Total vitrification appears to be the application of an extreme temperature evenly throughout the entire length or significant section of the rampart for a significant time, to the extent that the rock face of the rampart actually melts and forms a glassy or bubbled surface.  Craig Phadrig for example shows signs of intense heat vitrification along the entire 230m circumference of its interior rampart. Another example is Wincobank which has heat vitrification along its 430m rampart

Dating of Forts

Insert dating evidence Here.

Vitrified forts are notorious for their lack of strong dating evidence, recently however,

Materials available to burn

A number of excavations have unvieled the charred remains of wood used in the vitrification process, wood is known to burn at different temperatures, with Oak and Yew being the hottest available in the British Isles. An analysis of the wood remains will reveal the natural burning temperature of the wood, which coupled with details of the rock in question would indicate if the wood alone could have reached the correct temperature to perform vitrification.

A further factor is other materials used to help the vitrification process, these may include; salt has been suggested as capable of raising the temperature of the fire, some rocks may themselves give off minerals which could increase the temperature or act as a flux during vitrification. Furthermore there is evidence that some vitrified ramparts had an outer layer of smaller stones which became the outer vitrified layer. Presumably some additional material would have been required to ensure the smaller stones remained in contact with the rampart long enough for them to fuse.

Number of Ramparts/specific relationship between vitrified ramparts and others

Many vitrified forts have a double circular or oval rampart, with the inner vitrified. This may show them as having a cultural similarity and therefore allow us to tie together multiple forts to determine the spread of the culture.

Types of Rock used in Vitrification

Geographic Distribution

Analysis of the geographic distribution shows a marked trend towards a “Scottish homeland” for vitrified forts. With a few exceptions vitrified forts occur mainly in scotland, out of 260 hill forts in Scotland, 48 have been shown to have been classified as vitrified. Eslewhere in the british Isles vitrification is almost unknown. Even in Scotland vitrified forts tend focus to the north of the Forth.