Complex sentence: It is clear from its size that it was planned from the outset to be the cathedral of the diocese though the seat of the bishop moved between Wells and the abbeys of Glastonbury and Bath, before finally settling at Wells.
Split into simpler sentences: It is clear from the size of the building that it was planned from the outset to be the cathedral of the diocese. However, the seat of the bishop moved between Wells and the abbeys of Glastonbury and Bath, before finally settling at Wells.