The Acropolis is located on a flattish-topped rock that rises 150 m (490 ft) above sea level in the city of Athens, with a surface area of about 3 hectares (7.4 acres). While the earliest artifacts date to the Middle Neolithic era, there have been documented habitations in Attica from the Early Neolithic period (6th millennium BC).
Warrior wearing a boar tusk helmet, from a Mycenaean chamber tomb in the Acropolis of Athens, 14th-13th century BC.
There is little doubt that a Mycenaean megaron palace stood upon the hill during the late Bronze Age. Nothing of this megaron survives except, probably, a single limestone column-base and pieces of several sandstone steps. Soon after the palace was constructed, a Cyclopean massive circuit wall was built, 760 meters long, up to 10 meters high, and ranging from 3.5 to 6 meters thick. This wall would serve as the main defense for the acropolis until the 5th century. The wall consisted of two parapets built with large stone blocks and cemented with an earth mortar called emplekton (Greek: ἔμπλεκτον). The wall uses typical Mycenaean conventions in that it followed the natural contour of the terrain and its gate, which was towards the south, was arranged obliquely, with a parapet and tower overhanging the incomers' right-hand side, thus facilitating defense. There were two lesser approaches up the hill on its north side, consisting of steep, narrow flights of steps cut in the rock. Homer is assumed to refer to this fortification when he mentions the "strong-built House of Erechtheus" (Odyssey 7.81). At some time before the 13th century BC, an earthquake caused a fissure near the northeastern edge of the Acropolis. This fissure extended some 35 meters to a bed of soft marl in which a well was dug. An elaborate set of stairs was built and the well served as an invaluable, protected source of drinking water during times of siege for some portion of the Mycenaean period.
During the Hellenistic and Roman periods, many of the existing buildings in the area of the Acropolis were repaired, due to damage from age, and occasionally, war. Monuments to foreign kings were erected, notably those of the Attalid kings of Pergamon Attalos II (in front of the NW corner of the Parthenon), and Eumenes II, in front of the Propylaia. These were rededicated during the early Roman Empire to Augustus or Claudius (uncertain), and Agrippa, respectively. Eumenes was also responsible for constructing a stoa on the South slope, not unlike that of Attalos in the Agora below.
During the Julio-Claudian period, the Temple of Rome and Augustus, a small, round edifice, about 23 meters from the Parthenon, was to be the last significant ancient construction on the summit of the rock. Around the same time, on the North slope, in a cave next to the one dedicated to Pan since the classical period, a sanctuary was founded where the archons dedicated to Apollo on assuming office. During 161 AD, on the South slope, the Roman Herodes Atticus built his grand amphitheatre or Odeon. It was destroyed by the invading Herulians a century later but was reconstructed during the 1950s.
During the 3rd century, under threat from a Herulian invasion, repairs were made to the Acropolis walls, and the "Beulé Gate" was constructed to restrict entrance in front of the Propylaia, thus returning the Acropolis to use as a fortress.