The church was granted in AD 1154 to the Order of the Temple of Solomon. Soon afterwards they rebuilt the nave and chancel on the original Saxon plan with the walls in one straight line with the tower walls. They added the present north and south trancepts, originally walled off from the main church, as chapels for use of their members.
The chapel/south transept, more like a large porch, was built on to the church to the south side by the Templars for their own use in about 1180. Lower in level, square and solid as a Crusaders' castle, perhaps built by men who had fought hand to hand with the Saracens in the Holy Land, it has its own miniature chancel and sacristy and forms a complete church within a church.
Over the south doorway the great height of the arch is thought to have been designed to admit Templar banners. The Norman font of Sussex marble now stands on a modern pillar in the small chancel, out of which a door leads to the scaristy built between the chancels as a strong room to contain valuables.