According to Greek mythology, Troezen came into being as a result of two ancient cities, Hyperea and Antheia, being unified by Pittheus, who named the new city in honor of his deceased brother, Troezen. The ancient city of Troezen was one of the first cult centres in honour of the sea god Poseidon (in Greek mythology Poseidon is a forebearer of the former king Troezen after whom the city was named).
In 580 BC and in the face of the advancing Persian army Athenian general Themistocles proposed to the city assembly that all the women, children and elderly residents of Athens be evacuated to Troezen while able bodied men were sent to fight the Persians or to man the Athenian fleet. Although Athens was subsequently destroyed its citizens were spared.
During the Classical and Hellenistic periods numerous temples and other buildings were constructed in Troezen including a complex of buildings forming a sanctuary to Asclepius although this was somewhat overshadowed by its rival at nearby Epidauros. Other temples were dedicated to Artemis, Hippolytus, Athena and Aphrodite, traces of which can be found in a forest near Troizina.
In 230 BC the volcano at nearby Methana erupted causing severe earthquakes which destroyed many of the temples and buildings at Troezen leading to a decline of the sanctuary to Asclepius. During the Roman era many of these buildings were restored but as Christianity became predominant material from ancient buildings was used in the construction of churches as can be seen in the Diocese church which dates to the 6th century AD.
References:Visby Cathedral (also known as St. Mary’s Church) is the only survived medieval church in Visby. It was originally built for German merchants and inaugurated in 1225. Around the year 1350 the church was enlarged and converted into a basilica. The two-storey magazine was also added then above the nave as a warehouse for merchants.
Following the Reformation, the church was transformed into a parish church for the town of Visby. All other churches were abandoned. Shortly after the Reformation, in 1572, Gotland was made into its own Diocese, and the church designated its cathedral.
There is not much left of the original interior. The font is made of local red marble in the 13th century. The pulpit was made in Lübeck in 1684. There are 400 graves under the church floor.