 The curtain walls enclosing the castle show the multiple phases of construction at Peveril , with stonework from the Norman period – differentiated by the use of opus spicatum – to modern repairs . The walls were surmounted by walkways , which next to the gatehouse would have stood about 5 m ( 16 ft ) above the ground level immediately outside the castle . In the 12th century , a tower projecting less than 2 m ( 6 ft 7 in ) was added to the north wall . In Eales ' opinion , it " would have been of limited military value , compared with the boldly projecting towers of later castles " which allowed defenders to deploy flanking fire along the base of the walls . The land within the castle slopes downwards from west to east . Water storage would have been a concern for the garrison of the castle , but how they procured water is uncertain . 
