Cyclopean architecture is the name for the style of stone structures that are built of large rough blocks of stone, put together without mortar.
It was originally a term invented by the ancient Greeks to explain stone structures local to their area. The race of Cyclops, they thought, must have been strong enough to carry the stones and set them into place. There is a Cyclopean wall at the base of the Acropolis in Athens, and the Acropolis of Mycenae is also built in this style.
The term Cyclopean is generally used, though, to refer to any stone structures built without mortar, like the walls and buildings of Inca cities.