This shows carving of the highest order, most probably the  work of the Guild of  Masons, based in Canterbury.  Major and minor shafts with ornate capitals support an exquisite tympanum.  The main subject a Majestas Domini (Christ in Glory) is surrounded by three voussoirs:

1. The innermost is a narrow band of      foliage

2. The middle voussoir has fantastical representations of animals inspired by
medieval bestiaries

3. The outermost depicts more typical scenes of medieval life (possibly the labours of the months?) and a few with scriptural associations.

In the vesica, Christ raises one hand in blessing while the other holds an open book (the Bible?). He is surrounded above by Angels, two holding scrolls.  At one remove are coroneted heads of noble mortals, while at his feet are a sphinx, two amphibious creatures
(mermaids?) and a griffin.