Originally, the church appears to have consisted of a nave with two aisles. It had a wooden ceiling supported by six pillars. The building material was brick. The main entrance was probably located to the west, though side entrances may have existed in the north and south walls. Stylistically, the church was part of a group of brick churches built in the area around Lake Mälaren at the time, including Strängnäs Cathedral, St. Mary's Church, Sigtuna and . The church was successively rebuilt and enlarged during the 14th and 15th centuries. Embellishing the church was a way for both the monarchs of Sweden and the citizens of Stockholm to demonstrate their power and influence.