The cathedral has its origins in AD 672 when St Etheldreda built an abbey church. The present building dates back to 1083, and cathedral status was granted it in 1109. Until the Reformation it was the Church of St Etheldreda and St Peter, at which point it was refounded as the Cathedral Church of the Holy and Undivided Trinity of Ely, continuing as the principal church of the Diocese of Ely, in Cambridgeshire. It is the seat of the Bishop of Ely and a suffragan bishop, the Bishop of Huntingdon. Architecturally it is outstanding both for its scale and stylistic details. Having been built in a monumental Romanesque style, the galilee porch, lady chapel and choir were rebuilt in an exuberant Decorated Gothic. Its most notable feature is the central octagonal tower, with lantern above, which provides a unique internal space and, along with the West Tower, dominates the surrounding landscape. Ely Cathedral is a major tourist destination, receiving around 250,000 visitors per year, and sustains a daily pattern of morning and evening services.
Ely Abbey was founded in 672, by Æthelthryth (St Etheldreda), daughter of the East Anglian King Anna. It was a mixed community of men and women. Later accounts suggest her three successor abbesses were also members of the East Anglian Royal family. In later centuries the depredations of Viking raids may have resulted in its destruction, or at least the loss of all records. It is possible that some monks provided a continuity through to its refoundation in 970, under a Benedictine rule. The precise siting of Æthelthryth's original monastery is not known. The presence of her relics, bolstered by the growing body of literature on her life and miracles, was a major driving force in the success of the refounded abbey. The church building of 970 was within or near the nave of the present building, and was progressively demolished from 1102 alongside the construction of the Norman church. Ermenilda of Ely was an Abbess here, as well, after her husband Wulfhere of Mercia died in 675.
The cathedral is built from stone quarried from Barnack in Northamptonshire (bought from Peterborough Abbey, whose lands included the quarries, for 8000 eels a year), with decorative elements carved from Purbeck Marble and local clunch. The plan of the building is cruciform (cross-shaped), with an additional transept at the western end. The total length is 537 feet (164 m), and the nave at over 75 m (246 ft) long remains one of the longest in Britain. The west tower is 66 m (217 ft) high. The unique Octagon 'Lantern Tower' is 23 m (75 ft) wide and is 52 m (171 ft) high. Internally, from the floor to the central roof boss the lantern is 43 m (141 ft) high. It is known locally as "the ship of the Fens", because of its prominent position above the surrounding flat landscape.
Having a pre-Norman history spanning 400 years and a re-foundation in 970, Ely over the course of the next hundred years had become one of England's most successful Benedictine abbeys, with lands exceeded only by Glastonbury, a famous saint, treasures, library and book production of the highest order. However the imposition of Norman rule was particularly problematic at Ely. Newly arrived Normans such as Picot of Cambridge were taking possession of abbey lands, there was appropriation of daughter monasteries such as Eynesbury by French monks, and interference by the Bishop of Lincoln was undermining its status. All this was exacerbated when, in 1071, Ely became a focus of English resistance, through such people as Hereward the Wake, culminating in the Siege of Ely, for which the abbey suffered substantial fines.
Under the Normans almost every English cathedral and major abbey was rebuilt from the 1070s onwards. If Ely was to maintain its status then it had to initiate its own building work, and the task fell to Abbot Simeon. He was the brother of Walkelin, the then Bishop of Winchester, and had himself been Prior at Winchester Cathedral when the rebuilding began there in 1079. In 1083, a year after Simeon's appointment as abbot of Ely, and when he was 90 years old, building work began. The years since the conquest had been turbulent for the Abbey, but the unlikely person of an aged Norman outsider effectively took sides with the Ely monks, reversed the decline in the abbey's fortunes, and found the resources, administrative capacity, identity and purpose to begin a mighty new building.