The island of Syros used to be mostly Catholic, a result of the Venetian expansion in the Aegean. During the Greek War of Independence (1821-1828), it was granted the protection of the Vatican and served as the landing point of refugees from Chios, Psara and Crete. The refugees founded the city of Ermoupolis, now the administrative capital of the Cyclades, and changed the make up of the island which is now two-thirds Orthodox.
Even so, Ermoupolis still has an Italianate feel (neo-Palladian some might call it) rather than the strict Neoclassical feel of old Athens observed in Plaka and also Kea.
There used to be some tension between the two communities until 1970, when the Pope and the Patriarch of Constantinople reached an accord. Firstly, the two communities would observe Easter on the same date, the Orthodox one. Secondly, the children of mixed marriages would take up the religion of the father. There still are political parties and organisations, though, that are religion-based and Ermoupolis is an Orthodox enclave in a Catholic countryside.
The most important art treasure on Syros, was accidentally discovered in the Church of Dormition of the Virgin (NOT Assumption as some translate it – there are doctrinal differences, don’t ask) in 1983. It is a picture of – you guessed it – of the Dormition of the Virgin painted by none other than a young El Greco around 1562-1564, when he was 19-21. It is signed clearly by him, which makes it possibly the earliest work of El Greco in existence.
The painting – an icon that looks nothing like his later works, but more of the medieval Cretan school – is really superb, but that may just be me.