It is extremely difficult to assign a satisfactory reason for this peculiarity of English plans. It arises so suddenly, however, in the English churches of the Norman age that it must have pre-existed in those of the Saxons; though why they should have adopted it is by no means clear. If these churches had wooden roofs, which was almost certainly the case, their naves might easily have been wider, and it can hardly have arisen from any æsthetic motive. As we now judge them, these early naves were badly proportioned for hearing an address from the bishop or prior, and as ill adapted for a multitude to see what was passing at the altar; but for pictorial effect they surpass everything erected on the Continent, unless with greatly increased dimensions of height or width. Whether, therefore, it were hit upon by accident or by design, its beauty was immediately appreciated, and formed the governing principle in the design of all the English cathedrals. It was a discovery which has added more to the sublimity of effect which characterises most of our cathedrals than any other principle introduced during the Middle Ages. All the cathedrals above enumerated, indeed most of those which were designed by Norman prelates during the first half-century after the Conquest, were erected on very nearly the same plan as that at Norwich. Durham (1095-1133) was the first to show any marked deviation from the type[98] (Woodcut No. 804). The nave and choir became nearly proportioned to one another, and for the first time we see a distinct determination from the first that the building should be vaulted. All this involved an amount of design and contrivance which entirely emancipated us from the Continental type, and may be considered as laying the foundation of the English style. In addition to what was doing at Durham there prevailed an extraordinary activity in church-building in the North of England during the whole of the 12th century, owing to the erection of the great abbeys whose gigantic fossils still adorn every main valley in Yorkshire. As this part of the country was more remote from foreign influence than the South, the style developed itself there with a vigour and originality not found elsewhere; but its effect was appreciated, and when Lincoln was rebuilt, about the year 1200, the English style was perfected in all essential parts. This is even more remarkably shown, however, at Salisbury, commenced in 1220 and completed in 1258, with the exception of the spire, which does not appear to have formed part of the original design. [Illustration: 804. Plan of Durham Cathedral. (From Billings.) Scale 100 ft. to 1 in.]