One of around 500 wrought iron nuts and bolts that were replaced during a refurbishment of the aqueduct in 2003-4. The modern replacements were made of recycled iron.
Limestone quarrying has taken place in landscape of the World Heritage Site since the sixteenth century. The stone was burned with coal in kilns to make lime. This was used in plaster and cement for buildings or it could be scattered on fields as fertiliser. Limestone was also used in iron smelting.