Kastellorizo's cathedral, Agios Konstantinos kai Eleni (Μητρόπολη Αγίων Κωνσταντίνου και Ελένης, Metropolitan Church of Saints Constantine and Helena), was built in 1835, though its design seems more modern. The centre of the nave of the three-aisled vaulted basilica is lined by twelve monolithic granite columns taken from the temple of Apollo in the ancient Lycian city of Patara on the nearby Turkish coast.

The church stands on the north side of a precinct, enclosed by a low wall and iron railings, which also includes the Parthenagogeion (girls' school, built 1905) to the west of the church and the Santrapé Town School for boys (built 1903) to the east. The Santrapé school now educates all the island's children, of which there are sadly only few.

The central square of the precinct is known as the Avlogyro, which is has a typically Dodecanese choklakia mosaic floor (see next page). Most of the island's christenings, weddings and funerals are conducted here, and before and after the services the Avlogyro is lively and full of people.

Saints Constantine and Elena are considered very important by all the eastern orthodox churches (including Greek, Russian, Serbian and Bulgarian). The first Christian Roman emperor Constantine the Great (circa 272 - 337 AD) is said to have been converted to Christianity by a vision of the cross before a decisive battle. He made Christianity an official religion of the empire and founded the city of Constantinople (formerly Byzantium, today the Turkish city of Istanbul), which is still considered by Greeks to be the spiritual centre of their religion. In 325 he convened the first general council of the church (known as an Ecumenical Council) at Nicaea. Constantine was only baptised on his deathbed, but nobody seems to hold that against him.

His mother Agia Eleni (Saint Helena, circa 246/50 – 18 August 330) is said to have been very pious and charitable and to have discovered the True Cross on which Christ was crucified and other religious relics throughout the Roman Empire. For her efforts she has become the patron saint of archaeologists. Constantine built Church of the Holy Sepulchre at the place where she discovered the cross in Jerusalem, as well as churches at sites where she found relics. Her palace in Rome was later converted into the church Santa Croce in Gerusalemme.

Saints Constantine and Helena Day on 21 May is an important annual holy day on Kastellorizo, as in many places in Greece, and is celebrated with a service in the church, a formal ceremony and procession, and the blessing of Greek naval vessels.

See an icon of Saints Constantine and Helena in the Agios Giorgos Tou Pigadiou church, in Kastellorizo's main harbour on gallery page 101.