Old Sarum Cathedral, along with the Bishop’s Palace and Castle, were located within a former Iron Age hill fort. The 11th century church had an apse echelon plan with the apses of the aisles enclosed externally within square walls, a form repeated in the early 12th century reconstruction. Osmund’s church did not have full transepts, but seems to have had side towers in the position of transepts. A similar arrangement existed in the slightly later Norman cathedral at Exeter until its reconstruction in the 14th century. When the choir was rebuilt in the early 12th century the width of the main vessel in the east end was increased and large piers were built for a prominent central tower. Both these suggest that the intention was to replace the original, narrower, and presumably, lower nave of the 11th century church. However, the fall of Bishop Roger in 1139 allowed seven bays of the original nave to survive until the cathedral was abandoned in the 13th century. Excavations suggest that the original west façade was a simple screen, originally unembellished with towers.

Bishop Roger (1102-1139) rebuilt the choir, created full transepts with east and west aisles, built a treasury and laid out the cloister to the north of the new choir during the first four decades of the 12th century. The church built in the late 11th century was 173ft long from east to west and 113½ft across the ‘transepts’. As a result of Roger’s building campaign its overall size was increased to 316ft long and 138ft wide. The new, square, east end had a projecting central eastern chapel flanked by two smaller chapels. Though the chapels terminated in apses internally, externally they were treated as square blocks. Between the chapels, excavations revealed narrow spaces, the purpose of which is uncertain. A similar arrangement can be found in the later east end of Winchester Cathedral where the thickened sections between the chapels seem to be related to access to a proposed upper storey. An alternative interpretation is that the original layout included some form of raised floor within the central chapel that was removed later in the 12th century.

After Roger’s death a narthex was built at the west end of the nave by Bishop Jocelyn de Bohun (1142-84). It consisted of twin towers flanking a new west door and measured 75ft wide and 30½ ft deep. It was built in front of the former simple screen façade from the early Norman cathedral. The towers were markedly rectangular in plan, and a tower of a similar shape was built at St John’s in Devizes, a church which may have been associated with Bishop Roger.

Much of the stone of Old Sarum was reused in buildings near the site, in houses in Salisbury and in and around the new cathedral. The wall of the close includes dozens of reused carved stones. However, the major collections of carved stones are in the Salisbury and South Wiltshire Museum and the nearby store used by English Heritage. Separate entries have been compiled for these collections.

In 1075 an edict of the Council of London ordered the transfer of cathedrals to more populous places, leading to the unification of the sees of Ramsbury and Sherborne and the transplantation of the new see to the Iron Age hill-fort at Old Sarum. Immediately after the Norman Conquest, a timber, motte-and-bailey castle was established and ditches were dug running north to south, subdividing the area of the hill-fort. Within the north-west part of the fort the cathedral was erected.

Herman, who was the Bishop of Sherborne before 1075, then of Old Sarum from 1075 to 1078, probably began the construction of the new cathedral, but most of the work took place under his successor Bishop Osmund (1078-99). The cathedral at Old Sarum was consecrated on 5 April 1092, but five days later it was apparently struck by lightning and damaged, though this may be an attempt to gloss over a failure in the construction of the building.

Osmund's successor, Bishop Roger (1102-39) rebuilt the east end of the cathedral, creating one of the most richly decorated buildings of its day. Roger had served as a chaplain and steward to Henry I. In 1101 he was appointed as Chancellor, a position he relinquished when he became Bishop of Old Sarum in 1102, although his consecration did not take place until 1107. During his thirty-five year reign, Henry I spent seventeen years in Normandy and therefore needed reliable advisers to manage Royal affairs in England. Henry appointed Roger as Regent during his absence in 1123–6 and probably on other occasions.

After Henry I’s death in 1135 Roger accepted Stephen of Blois’ claim to the throne despite having sworn allegiance to Matilda in 1131. In 1139 Roger was summoned to see King Stephen at Oxford, and after a dispute, Roger was arrested. Roger was returned to Old Sarum, effectively as a prisoner where he died on 11 December 1139. Roger was buried in the cathedral at Old Sarum, and on 14 June 1226 his remains were transferred to the new cathedral in Salisbury.

Roger’s successor, Bishop Jocelyn de Bohun (1142-84), built a large west façade, the last substantial building works that took place on the cathedral. In the early 13th century some new buildings were built on the site. A New Hall was erected in the southern half of the inner bailey and a bakehouse was built south-west of the main gatehouse. However, by the end of King John's reign the practical problems of the cathedral sharing a cramped, secure castle site were proving insurmountable for the clergy. In April 1217 the Dean and Chapter petitioned to Pope Honorius III to move the cathedral and on 29 March 1218 papal consent for the move was granted. By 1219 a cemetery and a wooden chapel had been built near the site of the Salisbury Cathedral. The foundation stone of the new church was laid on 28 April 1220 and in 1226 the bodies of three bishops, Osmund, Roger and Jocelin, were moved to the new cathedral. By 30 July 1227 the official translation from Old Sarum took place. Part of the old cathedral was retained for use as the Chapel of St Mary and a chapel was still in use at Old Sarum as late as the 16th century. However, once the clergy had moved from the site, the slow but inevitable process of decline, ruination and the quarrying of stone began. In 1237 an order was given to take down the hall and other buildings belonging to the bishop to use the building material to repair the castle. In 1276 permission was given for stone from Old Sarum to be used in new buildings in Salisbury; in 1327 a licence was granted for the construction of a close wall and in 1331 Edward III allowed the chapter to use stone from the old cathedral and some of the former clergy houses for repairs to the new cathedral and the precinct wall.

John Leland described Old Sarum In the 1530s as 'This thing hath beene auncient and exceeding strong: but syns the building of New-Saresbyri it went totally to ruine.' By 1832 Old Sarum was 'only a green mound without a habitation upon it', but it was famous, or more accurately infamous, as one of the notorious rotten boroughs abolished in that year. The major campaign of excavations began on 23 August 1909 and would have lasted for a decade, but the outbreak of war in 1914 led to their immediate cessation.

For a more detailed discussion of the significance of Old Sarum and its sculpture, refer to Saunders (2012), the relevant volume of the Salisbury and South Wiltshire Museum Medieval catalogue.

Old Sarum was the dominant workshop in Wiltshire during the first forty years of the 12th century, an accolade that shifted during the third quarter of the century to Malmesbury Abbey. There is a link between the two workshops and it is likely that the architects of Malmesbury used Old Sarum as a template for their designs, as well as employing some of the craftsmen who became available after the dissolution of Bishop Roger’s workshop. The direct influence of Old Sarum can be detected in buildings in south Wiltshire and Somerset, while in north Wiltshire and the influence is probably indirect, via Malmesbury. However, at Leonard Stanley in south Gloucestershire some sculpture has the characteristics that can be found in some of the most accomplished carving at Old Sarum.

Old Sarum also has links through southern Wales, where it owned some land and its influence even spread into Ireland. There were also a number of buildings in the Midlands where similar detailing can be found. Foremost amongst these was Lincoln Cathedral, but others included Newark Castle and Kenilworth Priory. The presence of motifs from Old Sarum is probably due to Bishop Roger’s nephew being the bishop of Lincoln (1123-48).