The Parthenon was converted into a Christian church in the final decade of the sixth century AD to become the Church of the Parthenos Maria (Virgin Mary), or the Church of the Theotokos (Mother of God). The orientation of the building was changed to face towards the east; the main entrance was placed at the building's western end and the Christian altar and iconostasis were situated towards the building's eastern side adjacent to an apse built where the temple's pronaos was formerly located. A large central portal with surrounding side-doors was made in the wall dividing the cella, which became the church's nave, from the rear chamber, the church's narthex. The spaces between the columns of the opisthodomus and the peristyle were walled up though a number of doorways still permitted access. Icons were painted on the walls and many Christian inscriptions were carved into the Parthenon's columns. These renovations inevitably led to the removal and dispersal of some of the sculptures. Those depicting gods were either possibly re-interpreted according to a Christian theme, or removed and destroyed.
The Parthenon became the fourth most important Christian pilgrimage destination in the Eastern Roman Empire after Constantinople, Ephesos and Thessalonica. In 1018, the emperor Basil II went on a pilgrimage to Athens directly after his final victory over the Bulgarians for the sole purpose of worshipping at the Parthenon. In medieval Greek accounts it is called the Temple of Theotokos Atheniotissa and often indirectly referred to, as famous without explaining exactly which temple they were referring to, thus establishing that it was indeed well known.
At the time of the Latin occupation, it became for about 250 years a Roman Catholic church of Our Lady. During this period a tower, used either as a watchtower or bell tower, containing a spiral staircase was constructed at the southwest corner of the cella and vaulted tombs were built beneath the Parthenon's floor.