"A hillfort is a type of earthwork used as a fortified refuge or defended settlement, located to exploit a rise in elevation for defensive advantage. They are typically European and of the Bronze Age or Iron Age. Some were used in the post-Roman period. The fortification usually follows the contours of a hill and consists of one or more lines of earthworks, with stockades or defensive walls, and external ditches. Hillforts developed in the Late Bronze and Early Iron Age, roughly the start of the first millennium BC, and were used in many Celtic areas of central and western Europe until the Roman conquest."
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This construction almost always had circular plant. The older houses were mostly made of straw-mud and the newer ones of masonry. The roof was made of branches and mud and after long poles.