Sigtuna was a Christian city from the beginning. A bishopric was established in the middle of the 11th century. This ceased after about a hundred years in connection with the addition of the archbishop's seat in Old Uppsala. During the early Middle Ages, no less than six or seven mighty stone churches with associated cemeteries were built in Sigtuna. All but one, the cathedral, were behind the oldest built-up area and along a somewhat later laid-out street parallel to Stora gatan. Today, only parts of a once powerful west tower of St. Lars Church can be seen. A tower that was renovated in the late 16th century by Johan III. From archaeological excavations, however, it is known that the church was a large greystone church, probably built during the 12th century.

Source: https://destinationsigtuna.se/