When the Normans invaded England they brought with them a new form of stone construction. Many castles were constructed throughout England culminating in the building of the most iconic, Windsor Castle, in the late Norman period. The walls built at that time incorporated flat oyster shells bedded within the mortar joints and chips or flakes of stone pressed into the soft mortar, both of which materials are classed as gallets, a word derived from the French language.

The Norman castle at Windsor