The Acropolis (a term literally meaning "high city") is a hill in the centre of Athens containing many historically important buildings. It was first occupied during the Mycenaean period, and was important militarily because it was defensible and had springs which could provide water during a siege. Its military importance continued through the 19th century. The buildings on the Acropolis included several important religious buildings. Many of these buildings are important in the history of art and architecture as examples of ancient monumental architecture. The Acropolis is often evoked in literature and belles lettres as the epitome of classical art, and thus it is important for students to know about it in order to make sense of later references to it.