Final answer:
An edifice (option 3) is a large and significant building, often of public or religious importance. The term describes imposing structures such as the Athenian Acropolis. 'Mansion' and 'citadel' can also be types of edifices, but 'edifice' is more inclusive and apt for the question's description.
Step-by-step explanation:
A building, especially one of large size, massive structure, or imposing appearance, is best described by the term edifice. An edifice is a term used in architecture that refers to a large and usually significant building. For example, monumental architecture such as pyramids and temples are considered edifices because these are large structures built for public viewing or use. The Athenian Acropolis, with its ancient buildings including the Parthenon, is an example of an ancient citadel that also fits the description of an edifice due to its significant cultural and architectural impact.
While 'mansion' refers to a large and impressive residential home, and 'structure' is a general term for anything constructed or built, an edifice specifically suggests an imposing building often of public or religious significance. A 'citadel', similar to the Acropolis, is a fortress or fortified area and can be considered an edifice if it has an imposing and massive structure.
In contrast, the use of cyclopean masonry is a method of construction using huge, roughly shaped blocks of stone, which could be utilized in the building of such grand edifices. The term buttress is also related to architecture, describing a supporting structure that adds stability to a building. Hence, in the context of architecture, both 'mansion' and 'citadel' are types of edifices, but 'edifice' is the best choice for describing a building noted for its size and imposing appearance.