Poseritz Brick church is built on foundations of large fieldstones. There are individual fieldstone courses in the tower. Work on the nave began between 1302 and 1325. The structure was designed as a three aisle hall structure, and this plan was followed in the first phase of construction, visible in the applied columns to the left and right of the tower entrance. Those to the east were removed in widening the triumphal arch, when a broader choir than originally planned was added, which required cuts into the east wall of the nave. The outer walls originate from the three aisle hall church. But in the second phase of construction the church was finally erected in the form of a triple-bay hall with buttresses. The choir, nave, and sacristy have cross vaulting, applied columns supported outside by abutment piers. Choir with rectangular termination built shortly afterwards in the 14th century. The sacristy was added afterwards in about 1400 to the north between the choir and the east wall of the nave. Massive west tower dating from later than 1450 using existing denticulation, a polygonal spire being added in 1580. The west portal with its segmental arch has an old, nailed diamond pattern door. The interior is plastered in white.
Oldest furnishings and accessories are the 14th century limestone font and Gothic crucifix over the south portal from about 1400. Other furnishings include offertory box from the 15th century, bell from about 1500, large triumphal cross ensemble with 16th century cross, Mary and John from the 15th century, two wooden patron chairs from 1598 and 1600, memorial tablet from 1600, late Baroque carved altar from 1703, confessional from 1747 and Rococo pulpit by Jakob Freese, Stralsund, from 1755.
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.