sentences:  The 'bluestones' (of Ordovician dolerite) which form the lintels of Stonehenge were sourced in the Preseli Hills of Pembrokeshire around 2500 BC.Bronze Age and Iron Age peoples made extensive use of local materials in erecting a variety of cairns, standing stones and defensive works as manifest in Wales' many hill forts.Wales' many fine cathedrals, abbeys and castles have used a variety of stones in their construction; Caerbwdi Sandstone in St David's Cathedral, Old Red Sandstone at Llanthony Priory and Tintern Abbey, 'Blue Pennant' sandstone in Caerphilly Castle and Sudbrook Sandstone at Caldicot Castle to name but a few.