"Political considerations at Pergamon made it necessary to glorify the civic and religious center of the small city-state", Herbert Hoffmann observed in 1952. "The high podium served to impress the exalted position of the altar, situated as it was on a high elevation, upon foreign visitors as they approached along the plain to partake in the biennial festival of Athena Nikephoros".
Some fragments from the frieze (the back view of a Giant, probably from Worksop Manor, and a dead giant, found at Fawley Court have been identified), perhaps collected by William Petty, were part of Thomas Howard, Earl of Arundel's collection of Antiquities at Arundel House, Strand, London, but rejected, as too weathered, for inclusion in the gift to the Ashmolean Museum. However, the main excavation was carried out in two campaigns, in 1879 and 1904, and shipped out of the Ottoman Empire by the German archaeological team lead by Carl Humann; it was reconstructed in the Pergamon Museum in Berlin, built in part to receive it, from 1910, where it can be seen alongside other monumental structures such as the Market Gate of Miletus and the Ishtar Gate from Babylon.
The Altar has a 113 metre (371 feet) long sculptural frieze depicting the gigantomachy, or struggle of the gods and the giants. "the frieze is composed of a sequence of isolated, tightly-knit and self-contained groups and figures" each unit assigned to one workshop. Many inscriptions on the lower moulded margin identify the sculptor responsible and his city.
The Pergamene Altar, which consisted of a stepped square podium (remaining in situ, illustration, right) and an Ionic colonnade, synthesized in an innovative way two features of Ionian architecture and cult practice: the monumental open-air altar block raised on a podium, with Egyptian precedents, combined for the first time with features of the Ionic funerary monument or heroon of heroic ancestor-cult— the peristyle raised on a high podium. It forms the traditional fixed point against which the chronology of Hellenistic sculpture styles has been based. Unfortunately the date of the Great Altar is not secure; its two friezes (illustration, left) differ in their stylistic character, an anomaly that has been explained on the basis of their presumed chronological difference of twenty years (180-160 BCE). When the initial excavations were made, the chronology of Hellenistic pottery types had not yet been established. Another excavation in 1961 yielded some more ceramic material, which, if they are interpreted as downdating the altar's first construction to ca. 165 BCE, would associate it with Eumenes II's victories against Galatia in 167-166. Further test trenches in 1994 yielded yet more ceramic fragments, which were dated to just after 172 BCE, which would associate with the date of the recovery of Eumenes II from a reported assassination attempt at Delphi that almost cost him his life. Prevailing cautious opinion leaves its construction date open. Construction of the monument may have started as early as ca. 160 BCE.
Due to the pedantic nature of Hellenistic art, it has been theorized that the program of the external frieze of the Great Altar, which only partially survives, was deeply scholastic. The library at Pergamon was second only to Alexandria in the ancient world, and scholars such as Pergamon's own Krates of Mallos were probably commissioned to collaborate on its design. The original interpretation of Carl Robert and Otto Puchstein divided the four sides of the Great Altar's frieze into the realms of the Olympians (east), water and earth gods (west), celestial/light gods (south) and gods of night and constellations (north). Robert and Puchstein drew on three sources for their interpretation: Hesiod's Theogony, Bibliotheke, by the pseudo-Apollodorus and, for the north frieze, Phainomena by Aratos.
The interpretation that is currently most accepted is from Erika Simon's 1975 Pergamon und Hesiod, which draws exclusively on Hesiod's Theogony for a reading of the Great Altar. According to Simon, the frieze is arranged genealogically, with the descendants of Ouranos and of Ge, the Titans and Olympians, on the South and East friezes, respectively. On the left portion of the West frieze begin the descendants of Pontos, deities associated with water, who curl around to the right portion of the North frieze. Lastly are the descendants of Nyx, associated with darkness, mortality, and fate, who occupy the central portion of the North Frieze.
There are some inconsistencies with Simon's interpretation, such as the presence of Dione, mother of Aphrodite, who did not exist in Hesiod's Theogony but was instead a Homeric character. A more recent yet less respected interpretation by Michael Pfanner asserts that Nyx is in fact Persephone, as shown by the nearby presence of a pomegranate flower. In any event, of the near-hundred figures on the frieze surrounding the Great Altar, only fourteen have both name and position confirmed by surviving inscriptions; these include Athena and Ge (east), Aphrodite and Dione (north), Triton and a host of satyrs (west), and Themis and Asteria (south). Figures whose inscriptions have not been preserved but who may iconographically be identified beyond a doubt include Artemis, Zeus and Nike (east).
The Great Altar was probably constructed in the wake of Eumenes II's military victories over his opponents in the eastern Mediterranean and the mainland of Asia Minor. Pergamon sought to cultivate an image of itself as the inheritor of Athen's cultural and political legacy over the Greek-speaking world—Athens had fallen from primacy in the fifth century BCE, and no city-state had risen to replace it. Pergamene building projects aimed at this goal were extensive and included the sponsorship of monuments on the distant Acropolis and other Greek city-states in Asia Minor. The gigantomachy frieze on the Great Altar bolsters these claims by making direct reference both to the Parthenon at Athens and Attalid naval victories over Hannibal of Carthage. Most significantly, the extensive theme of Greek gods defending a natural order against the Giants who represented chaos paralleled the Attalid conception of the Pergamene dynasty as defenders of Greek culture against Gallic barbarians.
On the interior of the great altar is a separate frieze depicting the life of Telephos, son of Herakles, whom the ruling Attalid dynasty associated with their city and utilized to claim descendance from the Olympians and links with mainland Greece. Pergamon, having entered the Greek world much later than their counterparts to the west, could not boast the same divine heritage as older city-states, and had to retroactively cultivate their place in the Greek tradition.
The Nazi-era architect Albert Speer used the Pergamon Altar as the model for the Zeppelintribüne, 1934-37. The Führer's pulpit was in the center of the tribune. After World War II the frieze reliefs were translocated to the Hermitage Museum, ostensibly as a compensation for damage inflicted by the German invaders on Soviet museums. At the behest of Nikita Khrushchev, the frieze reliefs were returned to East Germany, together with the entire collection of the Dresden Gallery, in 1956.