For over 200 years we have been raised – especially in Germany and ignoring Nietzsche – on an idealized picture of classical Greek religion and art. The sulbime beauty of the Parthenon stood like a beacon in my imagination: Athena, sprung from the head of Zeus, was the personification of a synthesis of female sensitivity and male rationality. To my great surprise, when I first came face to face with the Parthenon in 1953, I sensed a dark, blood-drenched secret surrounding the building - for which I only found an “explanation” in 2013.
Floorplan of the Parthenon, indicating the Frieze, from columbia.edu
The Parthenon's name derives from the Greek word "παρθενών" (parthenon), which referred to the "unmarried women's apartments" in a house and in the Parthenon's case seems to have been used at first only for a particular room. The foundations of a small shrine have been excavated within the building, on the site of an older temple dedicated to Athena. However, the Parthenon never hosted the cult of Athena Polias, patrona of Athens: the cult image, which was bathed in the sea and to which was presented the peplos, was an olivewood xoanon, located at an older altar on the northern side of the Acropolis. The cella of the Parthenon housed the collossal, chryselephantine statue of "Athena Parthenos" sculpted by Phidias, but it was not related to any cult, nor was Parthenon an attribute of Athena (the "Virgin Goddess" was Artemis).
Quite independent of its interpretation the Parthenon
Frieze is the defining monument of the High Classical
style of Attic sculpture.
The Ionic frieze runs around the exterior walls of the cella, the inside structure of the Parthenon. Ten meters above the floor and in the shadow of the outer colonnade of the sanctuary, it received no sun and was hard to see by the visitor. For example, Pausanias did not see it and does not mention the frieze in his description of the Parthenon.
The bas-relief frieze was carved in situ; it was dedicated in 438 BC. Of the 160 m length of the original frieze, 130 m survive. It is composed of 114 blocks of 1 meter in height and an average 1.22 meters in width, showing 378 figures and 245 animals in procession in two parallel files (north and south walls).
The conventional interpretation of the Parthenon frieze is that it depicts the Greater Panathenaic Festival procession from the Leokoreion (a burial shrine for three virginal sacrifices!) to the Acropolis. This contention solved nothing and is fraught with problems; only in recent years has an alternative thesis emerged in which the frieze depicts the founding myth of the city of Athens instead of the festival.
The center of the Frieze over the Eastern Door to the Cella: “The Peplos Scene”, photo Wikipedia
The culminating event of the procession are five figures on the east side: three girls and two adults, an older man and a woman. The man, is Shoing a piece of cloth to the youngest girl on the right. This is usually assumed to be the presentation of Athena’s peplos, perhaps by the arrhephoroi.
A recent interpretation by Joan Breton Connelly identifies the
central scene on the east frieze (above the door to the cella, the
focal point of the procession) not as the handing over of Athena’s
peplos, but the donning of sacrificial garb by the daughter of King
Erechtheus in preparation for the sacrifice of her life. This
interpretation rests on the text of a fragmentary papyrus of
play "Erechtheus" where the sacrifice of the life of
Erechtheus' youngest daughter is demanded by the Delphic oracle in
order to save the city from destruction by the Eleusinians under
Eumolpos. Eumolpos, a son of Poseidon, was trying to take revenge for
the choice of Athena as protector of Athens over his father.
In her paper Joan Breton Connelly [Parthenon and Parthenoi, American Journal of Archaeology, AJA 100  53-80, available through JSTOR] argues most conincingly that the two adults are mythical King Erechtheus with the sacrificial shroud and his wife Praxithea standing with him, the parents of the three girls. The youngest, Pandora, is preparing to be sacrificed by her father. Her sisters, carrying sacramental gifts, had taken an oath that they would die with her. Pandora was killed by Erechtheus, who was victorious over Eumopolos, and Athens was saved....Pandora's sisters later jumped from the Acropolis to their death, and Erechtheus was swallowed by an earthquake staged by Poseidon.
In Greek mythology the sacrificial victims seem to have always been virgin daughters, viz. Iphigenia, daughter of Agamemnon and Makaria, daughter of Herakles. Both were to die to appease Artemis, who snatched them away and made them immortal companions of herself. My great idol Athena did nothing the like, she instructed Praxithea to build a memorial for the three girls on the Acropolis and made her the first priestess of the Parthenon and the Erechtheion.
Another example of sacrificial victim was Polyxena, daughter of King Priam of Troy. Of her death exists a vase painting that shows how Pandora might have ended, wrapped up in the shroud her father is holding.