Olena (Ὤλενα, today Oleni) became an episcopal see in Byzantine times, being recorded as the see of Bolaina (Βολαίνα) since the 9th century in the Notitiae Episcopatuum of the Patriarchate of Constantinople.
It was probably established after the reconquest of the Peloponnese from the Slavs, and was a suffragan of the Metropolis of Patras.
[1] The see remains attested in the Notitiae until the 13th century, but following the Latin conquest of the Peloponnese and the establishment of the Principality of Achaea, it was taken over by a Roman Catholic bishop.
On the demand of Prince Geoffrey I of Villehardouin, however, its seat was moved to Andravida, the Principality's capital.
[2] The Latin see was suppressed when the Principality was conquered by the Despotate of the Morea in 1430, and a Greek Orthodox residential bishop once again took up seat there.