Originally there was a chapel situated on the site of the current Aa-kerk church. This chapel was devoted to Mary and to Saint Nicholas, the patron of the bargees who cast off the vessels at the Westerhaven.
In 1247, the chapel became the parish church and was named Onze Lieve Vrouwe ter Aa (Our Lady at the Aa) - Aa being the nearby river. Groningen had two centers at the time. One of them was around the chapel. Here lived the fishermen and the traders. Between 1425 and 1465, the chapel was changed into a brick church with a transept.
Images of the Siege of Groningen in 1672 show Der Aa-kerk without the top of the tower. After the war a new wooden tower top was built. On 23 April 1710, the tower spontaneously collapsed killing two people. In 1711, a new tower was built.
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.