A type of Roman earthwork defence. It is a curved continuation of a bank and ditch around a marching camp so it came in where the entrances where. This is named after the curved collarbone - the clavicle. This prevented an enemy storming a gateway and running unopposed down the length of a camp. They were used on marching camps and temporary camps as they were a quick form of defence. Examples can be seen at Chew Green, Northumberland, for the 'construction' camp.