Changes in the Middle Ages
The first major change to the nave came in the 14th century, when the west tower was added. The central tower was probably taken down at this time, perhaps because it had become structurally unsound. This must have left the east end of the nave looking a bit messy, as the scars where the central tower had been would have been very visible.
So, a few years later in the 15th century, the parishioners began a major programme of works. They added the porch over the south door. Then they rebuilt the whole north arcade, including the transept arch. They also rebuilt the south transept arch, and added the clerestory.