Aardenburg oldest building is the reformed church, which until 1604 was used by the catholics and known as the St. Bavo. The western part of the church dates from the 13th century, when a new church was built on the foundations of an earlier Romanesque church which was built in the year 959 by monks from Gent and which burnt down in 1202. In Flanders, of which Aardenburg was part then, churches were built in the Schelde-Gothic style, an early variant of Gothicism that still featured Romanesque elements. This church is the most complete example of this style in the Netherlands. Characteristics of this style present in this church are the (reconstructed) tripartite west window, the early Gothic lancetwindows of the clerestorey, the triforium with coupled columns and the polygonal stair-turrets that flank each transept-arm. The shape of the windows of the side-aisles and the lower parts of the transept are still closer to Romanesque than to Gothicism. It is possible that stones from the former Roman castellum have been used in the oldest parts of the church.
In the 14th century the choir was replaced by a new one, a hall-choir consisting of three aisles of equal height, in a more mature Gothic style. Only the middle aisle extends at the back and has a polygonal closure.
When the protestants took the building in 1604 it was damaged too much for immediate use. The tower was repaired in 1607 while the roofs of the nave and side-aisles weren't renewed until 1626 and 1628 respectively. In 1646 a lantern was built on top of the tower.
In 1944 the church was badly damaged. When the upper part of the tower fell on the church in 1945 this caused even more damage. From 1947 until 1956 the church was restored. Work included the reconstruction of the tripartite window, traces of the previous round-topped window are still visible, as well as of the upper part of the facade. The upper part of the tower, with the lantern, was rebuilt in 1954-1956.