Rough stone

Unshaped or roughly broken stone, quarried locally or cleared from fields. It was laid as rubble in lime mortar to build the thick walls of castles, churches and manor houses, with better cut stone kept for corners, doorways and windows. Using rubble was far cheaper than dressed stone, and many twelfth-century churches show rubble walls with dressed stone detailing.

Sources: historicengland.org.uk · canterbury-archaeology.org.uk