Arequipa is known as Peru’s “White City” because much of its historic architecture uses pale volcanic sillar stone.
Sillar is a light-colored volcanic rock, sometimes pink, formed from deposits associated with volcanic activity in the region. Builders used it extensively for churches, mansions, courtyards, arches, and vaulted roofs, giving central Arequipa a visually unified appearance.
The city was founded by the Spanish in 1540, and sillar became especially important after earthquakes demonstrated the need for durable construction. Many historic buildings feature thick walls and heavy masonry, while the scarcity of timber encouraged the use of stone vaults instead of wooden roofs.
The nickname does not mean every building in Arequipa is white or made entirely from sillar. Adobe, brick, lime, and other materials were also used, and many colonial structures were rebuilt after earthquakes. The historic center, including the Santa Catalina Monastery and the Cathedral, was inscribed as a UNESCO World Heritage Site in 2000.