1066: William the Conqueror invades Saxon England.
1080: William de St Calais, a Benedictine abbot from Le Mans, France, is drafted to Durham. Bishop de Calais starts Normanising the locals. His programme combines legislation, re-education, job creation and, in 1093, building.
Durham Cathedral is marked out by historian Nikolaus Pevsner as the first high-profile Anglo-Norman building constructed in England. Its size - 61m long and 12m wide in the nave, with an overall internal length of 117m and a 66.5m tower - gave powerful representation to a new religious and political order.
Durham Cathedral's cruciform plan, and the way in which its principal nave/choir aisle is flanked by arcades, is firmly within the tradition of Norman church design. Its claim to historical fame lies in three main technical innovations which became integral to Gothic architecture 50 years later. It introduced pointed vaults, ribs and the concept of the flying buttress. It was a milestone in the paring down of structure and maximisation of internal space.
The Romans developed groined barrel vaults - achieved by crossing a longitudinal and a lateral barrel vault - to free architecture from continuous supporting walls. Load generated by a groin-vaulted roof is transmitted via the groins to columns. As designers sought to realise more ambitious structures however, these vaults posed problems.
Wider spans needed increasingly massive supporting columns to withstand lateral thrust.
The builders of Durham Cathedral wanted a high, wide nave with elegant columns. To achieve height they introduced pointed vaulting which directed structural loads more directly downward and helped minimise outward thrust. Reducing the span of transverse vaults limited the outward thrust exerted on end walls further still. For width, a high-level buttress was introduced to transmit the large lateral forces generated by the wide span of the principal, longitudinal vault to the cathedral's massive side walls.
These proto-flying-buttresses are enclosed by the roof covering the cathedral's arcades. However, they anticipate the exterior buttressing of later generations of cathedrals.
Transverse and diagonal stone ribs following the lines of groins had been used on small vaulted roofs before. But Durham Cathedral saw ribs used on a large scale project for the first time. Damage to ribbed groin- vaulted roofs during second world war bombing campaigns demonstrated that the ribs were not crucial to the roof vault's structural integrity. But there is broad agreement that stone ribs played a vital supportive role in vault construction as permanent centring as well as being decorative.
Ribs were constructed as free-standing arches which were used to support wooden and lath formwork. Between 12 and 20 inches of coursed rubble and lime-mortar slurry were laid on this formwork to create the vault shells. A plaster finish was applied after the wood and lath had been removed.
Durham Cathedral was substantially built within 35 years, by 1133, but was not fully completed until 1448.
Little documentation of the construction has survived 900 years. But historical evidence from other sites suggests that foremen would have directed the work of nearly 4,000 labourers and craftsmen with the aid not of drawn plans, sections and elevations, but from detailed written instructions. This would have been backed up with supporting drawings: in the building of Wells Cathedral a plaster floor was used to inscribe detailed diagrams illustrating structural principles and providing patterns from which oak and elm templates were made.
The regularity of stone courses making up the cathedral's exterior walls indicates close communication and tight quality control between quarry and site.
Durham, like many later cathedrals, would cause modern engineers grave anxiety, however. Though it was built on a rock platform, excavations show foundations stop 1.2-2m short of solid rock.