The mere fact that the detached tower was built suggests many
questions which are not easily solved. Why was it at all necessary?
Perhaps the cathedral bells hung in the south-west tower, and those of
the sub-deanery church in the other, or _vice-versa._ At all events,
we know that in the fifteenth century the sub-deanery church was
removed from the nave to the north arm of the transept. The great
window of the north end of the transept is also early fifteenth
century in date, and the detached tower likewise. Angle turrets were
placed upon the four angles of the transept during the same century;
and if Daniel King's drawing of 1656 is any guide, the tops of the
central and western towers had battlemented parapets added during the
same period. In any case, it appears that it took much longer to
complete the repair of the central tower than that at the south-west.
In fact, it is doubtful whether the former was finished until about
the end of the thirteenth or the beginning of the fourteenth century,
for its fall apparently wrecked much of the vaulting of the transept;
and this, from the character of its moulded and carved vaulting ribs
in the south arm of the transept, is of the same date as the rose
window in the east gable of the presbytery, the rose windows in the
east gables of the lady-chapel and the chapels at the east end of the
north and south aisles of the choir. This argues that at the end of
the thirteenth or the beginning of the fourteenth century, during
Bishop Leophardo's episcopate, these works were completed.

About the middle of the fifteenth century a stone rood screen was
built up between the western piers of the central tower. It thus
separated the choir under the crossing from the nave; but through the
middle of this screen there was an open archway with iron gates. On
either side, as parts of the screen, to the north and south was a
chapel, each with its altar. This new work had been known as the