A donation to the church in 1346 by King Magnus IV and his wife Blanche of Namur probably indicates that the first of a number of chapels had been added to the church. This chapel was originally dedicated to Saint Mary and was located at the south side of the east end of the church. The four bays that belonged to the chapel are still discernible in the interior of Storkyrkan. Similar chapels were built at approximately the same time at Visby Cathedral and St. Mary's Church, Lübeck. The chapel was decorated with Early Gothic murals in a style unusual for Swedish churches (later heavily restored). A second chapel was added to the church sometime before 1361, and further chapels were built during the early 15th century. By the end of the Middle Ages, Storkyrkan contained more than 30 chapels or specifically dedicated altarpieces, an amount only comparable with the cathedrals of medieval Sweden. The church thus grew piecemeal by the addition of chapels. Another set of murals, painted by Albertus Pictor and decorating the south west vaults (the paintings are currently not visible from the floor of the church) was also added during the 15th century. Between 1474 and 1496, a major reconstruction of the church was carried out which then incorporated these chapels into a single, unified space and installed new vaults, creating a uniformly high ceiling. The church was at approximately the same time also substantially expanded toward the east, while a choir was also added. This was partially because the church had become too small for the growing population of the city. The choir was demolished during the 16th century. The tower was also built in the early 15th century and was originally intended mainly as a defensive tower. By the end of the 15th century Storkyrkan had acquired the basic shape and size that it still has.