Vitrified Rock from Dun Lagaidh
Ullapool Museum

This small piece of rock may not look very special, but it is actually from the fort of Dun Lagaidh.  

Around the twelfth century, Dun Lagaidh was refortified from a simple wooden fort to a stone Dun. Dun Lagaidh appears to have been constructed by vitrification, in which two stones are fused together by immense heat. 

Most Duns were located at the top of hills and Dun Lagaidh matches this, being placed atop a rocky oval hill. These positions provided an instant power to such forts, as highly defendable positions in the medieval period. Often made to appear like embankments themselves, weaker parts of the forts would be reinforced with extra layers of vitrified walling.  

The use of vitrification in building this fort, a practice used at a range of Scottish castles, would have saved a great deal of cost in buying and transporting the mortar which would have been required otherwise. Instead, the stones were melted together through massive bonfires to provide the high heats required.