Circeii was an ancient Roman city on the site of modern San Felice Circeo and near Mount Circeo, the mountain promontory on the southwest coast of Italy. The area around Circeii and Mount Circeo was thickly populated with Roman villas and other buildings, of which the remains of many can still be seen.

Cyclopean masonry is a type of stonework found in Mycenaean architecture, built with massive limestone boulders, roughly fitted together with minimal clearance between adjacent stones and with clay mortar or no use of mortar. The boulders typically seem unworked, but some may have been worked roughly with a hammer and the gaps between boulders filled in with smaller chunks of limestone.