Archbishop Courtenay was licensed to build a Collegiate Church in 1395. He died in 1396 and the building was continued by Archbishop Arundel in 1396-1398. The college was for a master and 24 chaplains.
The main surviving building consists of the Gatehouse and to the west of it, the Refectory, Kitchen and Scullery with the Dormitory and Infirmary above.
It is of Kentish ragstone in Perpendicular style. The gatehouse is a 3 storeyed square building containing pointed stone carriage and pedestrian arches on the ground floor and castellated parapet above. Square-headed windows of 2 trefoil-headed lights each with dripstones over, those on the top floor having 2 tiers of such lights. Stone ribbed tierceran star vaulting beneath the arches. On the left of the entrance arch is a 2-storeyed room with oven probably used for baking bread to be distributed as alms at the gate.
Joining this to the west is a 2-storeyed range with 6 square-headed windows containing pairs of cinquefoil-headed lights but no dripstones over. Tiled roof. Stringcourse. Stone chimneybreast in the centre of the north front with modern red brick stack above it. 3 storeyed tower at the west end of the building known as the River Tower with the Muniment Room on the top floor. Similar windows to the rest of the building and castellated parapet over.