A hillfort is a type of prehistoric fortification consisting of one or more lines of earthwork (fort) on a raised area of land (hill), which was used to defend settlements in Bronze and Iron Age Europe. The defensive earthwork structure contains ramparts made of earth, stone, and/or wood, with an external ditch. Vitrified hillforts refer to those composed of stone ramparts bound together by a glassy material produced by heating rock, which partially melts and then vitrifies upon rapid cooling.

But how could rock be transformed into glass using prehistoric technology, when mineralogy indicates that partial melting temperatures exceed 1,100°C? Questions like these continue to mystify archaeologists and geoscientists. While some researchers think that vitrification of pre-existing hillforts occurred due to natural events (e.g., lightning) or enemy attack, others believe it was done deliberately during construction for defensive reasons.