The eastern arch is larger, with a pointed head and mouldings similar to those of the north arcade, again indicating a 15th century date. Between the two types of arches is a short length of plain wall, which gives us a very important clue to the development of both aisles.
'... the transepts predate the c.1200 south aisle, and may have been Anglo-Saxon ...'
It tells us that when the south arcade was built in c.1200, there was already something where the present large arch is now. Otherwise, the arcade would have continued right up to the east end of the nave. This ‘something’ was almost certainly an arch leading into a transept like the one still existing on the north today.
Therefore, the transepts predate the c.1200 south aisle, and may have been Anglo-Saxon, like the nave. The transepts probably flanked a central tower (a common feature in larger Anglo-Saxon churches), as remains interpreted thus have been found under the floor of the east end of the nave. This means that the Anglo-Saxon church was cruciform, although the nave did not yet have aisles.
So, not only was there a church here at the time of the Conquest, but it was a very large and important church. Perhaps that isn’t surprising, as Kirtling was owned by Harold Godwinson, the English king.