This church, dedicated to the Transfiguration of Christ, is at the same time, the Metropolitan Cathedral of Ermoupoli and the first to be built in the newly constructed city. Its construction began in 1824 and originally, the refugees from the most suffering parts of Greece at that time, had dedicated the church, to Christ our Saviour, as an act of gratitude for their deliverance. This three-naved basilica was completed in 1831, after a fundraise for this purpose. The name of the architect is unknown; however, this church bears resemblance to Panaghia tis Tinou (or our Lady of Tinos, one of the most important shrines of Greek Orthodox Christianity) which was built in 1823 by architect Efstratios Smyrnaios.
The church is situated in a stone built courtyard, on a high platform with metal railings on the southeastern side, whilst on its western side, it lies on a two storied construction with a vaulted monumental gallery which leads to an opening in Omirou Street. The courtyard has two spaces, paved with inset pebbles that form a beautiful mosaic. The one in the east, was used for reunions. It is worth saying that it was in this courtyard that Ermoupoli was given its current name, after an official assembly. The courtyard on the west side was used between 1824 and 1834 as a cemetery. Anthimos Gazis, a very important personality of the Modern Greek Enlightment, was buried here, in 1828, and his remains were found in a crypt in the west side of the courtyard. A marble memorial plaque dating from 1930 indicates the exact location of the burial, which is no longer reachable.
The two storied building on the west had rooms for the priests, the caretakers of the church as well as some hospices for the poor. It had also been used as a hospital, however, nowadays, these rooms are used for administrative and other purposes of the church. Over the years, clumsy restoration work and modifications have altered the original form of the church. More specifically, in 1917, the vaulted gallery that led to the main entrance was blocked. Only an embedded commemorative inscription indicates the original entrance. Many architectural and constructional elements of this church express the difficulties of that time, along with the symbolic significance of the Transfiguration of Christ.
On the east side, one can see the commemorative busts of some metropolitan bishops of Syros. The interior architecture of the cathedral is equally interesting, as well as the ecclesiastical wood carved furniture and the holy icons dating from the 19th century.
The annual celebration of the church is held on the 6th of August.