(The text of the Architecture and History pages is taken, with only very minimal changes, from Ruth Nineham’s “Church of St Mary the Virgin, Iffley, Historical Guide”, which is available as a printed and illustrated booklet for sale in the church for £3).
This did not include the present Chancel (which was added in the thirteenth century). The original ground plan was based on squares and rectangles geometrically related to each other in one of the favoured ratios of the middle ages, one to the square root of two. Some say the perfect proportions were intended to reflect the harmony of heaven, while others say the proportions were arrived at for practical reasons.
They point out that when the builders were measuring out the ground plan on the site itself, they used ropes and pegs. They measured the diagonal of the square baptistery, and used it as a suitable length for the nave. This is in fact one to the square root of two. It is unlikely that the plans for the church were previously drawn on vellum.