The Acropolis of Athens (Ancient Greek: ἡ Ἀκρόπολις τῶν Ἀθηνῶν, romanized: hē Akropolis tōn Athēnōn; Modern Greek: Ακρόπολη Αθηνών, romanized: Akrópoli Athinón) is an ancient citadel located on a rocky outcrop above the city of Athens, Greece, and contains the remains of several ancient buildings of great architectural and historical significance, the most famous being the Parthenon. The word Acropolis is from Greek ἄκρον (akron) 'highest point, extremity' and πόλις (polis) 'city'. The term acropolis is generic and there are many other acropoleis in Greece. During ancient times the Acropolis of Athens was also more properly known as Cecropia, after the legendary serpent-man Cecrops, the supposed first Athenian king.

While there is evidence that the hill was inhabited as early as the 4th millennium BC, it was Pericles (c. 495–429 BC) in the fifth century BC who coordinated the construction of the buildings whose present remains are the site's most important ones, including the Parthenon, the Propylaea, the Erechtheion and the Temple of Athena Nike. The Parthenon and the other buildings were seriously damaged during the 1687 siege by the Venetians during the Morean War when gunpowder being stored by the Turkish rulers in the Parthenon was hit by a Venetian bombardment and exploded.

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 ha (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).

There can be little doubt that a Mycenaean megaron palace stood upon the hill during the late Bronze Age. Nothing of this structure survives except, probably, a single limestone column base and pieces of several sandstone steps. Soon after the palace was constructed, a massive Cyclopean circuit wall was built, 760 meters long, up to 10 meters high, and ranging from 3.5 to 6 meters thick. From the end of the Helladic IIIB (1300–1200 BC) on, 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.

Not much is known about the architectural appearance of the Acropolis until the Archaic era. During the 7th and the 6th centuries BC, the site was controlled by Kylon during the failed Kylonian revolt, and twice by Peisistratos; each of these was an attempt directed at seizing political power by coups d'état. Apart from the Hekatompedon mentioned later, Peisistratos also built an entry gate or propylaea. Nevertheless, it seems that a nine-gate wall, the Enneapylon, had been built around the acropolis hill and incorporated the biggest water spring, the Clepsydra, at the northwestern foot.

A temple to Athena Polias, the tutelary deity of the city, was erected between 570 and 550 BC. This Doric limestone building, from which many relics survive, is referred to as the Hekatompedon (Greek for "hundred–footed"), Ur-Parthenon (German for "original Parthenon" or "primitive Parthenon"), H–Architecture or Bluebeard temple, after the pedimental three-bodied man-serpent sculpture, whose beards were painted dark blue. Whether this temple replaced an older one or just a sacred precinct or altar is not known. Probably, the Hekatompedon was built where the Parthenon now stands.

Between 529 and 520 BC yet another temple was built by the Pisistratids, the Old Temple of Athena, usually referred to as the Arkhaios Neōs (ἀρχαῖος νεώς, "ancient temple"). This temple of Athena Polias was built upon the Dörpfeld foundations, between the Erechtheion and the still-standing Parthenon. The Arkhaios Neōs was destroyed as part of the Achaemenid destruction of Athens during the Second Persian invasion of Greece during 480–479 BC; however, the temple was probably reconstructed during 454 BC, since the treasury of the Delian League was transferred in its opisthodomos. The temple may have been burnt down during 406/405 BC as Xenophon mentions that the old temple of Athena was set afire. Pausanias does not mention it in his 2nd century AD Description of Greece.

Around 500 BC the Hekatompedon was dismantled to make place for a new grander building, the Older Parthenon (often referred to as the Pre-Parthenon or Early Parthenon). For this reason, Athenians decided to stop the construction of the Olympieion temple which was connoted with the tyrant Peisistratos and his sons, and, instead, used the Piraeus limestone destined for the Olympieion to build the Older Parthenon. To accommodate the new temple, the south part of the summit was cleared, made level by adding some 8,000 two-ton blocks of limestone, a foundation 11 m (36 ft) deep at some points, and the rest was filled with soil kept in place by the retaining wall. However, after the victorious Battle of Marathon in 490 BC, the plan was revised and marble was used instead. The limestone phase of the building is referred to as Pre-Parthenon I and the marble phase as Pre-Parthenon II. In 485 BC, construction stalled to save resources as Xerxes became king of Persia, and war seemed imminent. The Older Parthenon was still under construction when the Persians invaded and sacked the city in 480 BC. The building was burned and looted, along with the Ancient Temple and practically everything else on the rock. After the Persian crisis had subsided, the Athenians incorporated many architectural parts of the unfinished temple (unfluted column drums, triglyphs, metopes, etc.) into the newly built northern curtain wall of the Acropolis, where they served as a prominent "war memorial" and can still be seen today. The devastated site was cleared of debris. Statuary, cult objects, religious offerings, and unsalvageable architectural members were buried ceremoniously in several deeply dug pits on the hill, serving conveniently as a fill for the artificial plateau created around the Classical Parthenon. This "Persian debris" was the richest archaeological deposit excavated on the Acropolis by 1890.