Horsted Keynes is an ancient parish in the centre of Sussex, covering about 5,000 acres (2,020 ha) of heavily forested, mostly rural land which forms part of the Weald. Nearly 480 acres (194 ha) was originally part of the ancient Forest of Anderida, and the soil consists of Hastings Sand and clay with several prominent sandstone ridges. The village stands on one of these. At the time of the Domesday survey in 1086, the parish of Horstede was in the Hundred of Ristone[note 1] and the Rape of Pevensey. Sir William de Cahaignes held all the land in the parish, and a Saxon noblewoman called Wulfgifa was the tenant of most of it. The name, derived from the Old English for "place where horses are kept", was later recorded as Orsteda (in 1121) and Horsestud (1190). To distinguish it from another parish called Horsted in the Rape of Pevensey, the names Grethorsted[note 2] or Horsted Magna were occasionally used for ecclesiastical purposes. The name that entered regular use, though, was Horsted de Cahaignes—later simplified to Horsted Keynes—in honour of Lord of the Manor and principal landowner Sir William de Cahaignes, an associate of Robert de Mortain who also held much land in Cahaignes in Normandy.
Many Sussex churches stand on high ground overlooking their village, but at Horsted Keynes the church was built in a deep dip to the north. This is because the original church on the site—a small wattle and daub structure, later succeeded by a wooden church built from the oak trees prevalent in the Forest of Anderida (a pattern repeated at many villages in the Sussex Weald)—occupied a pre-Christian site of pagan worship. St Giles' Church "may be one of the best examples of re-use of an old religious site" which was again a common practice in Sussex: the present building, like its wooden and wattle and daub predecessors, stands within a stone circle which can still be seen in places, and which probably contained a pagan temple. This may also explain its unusual orientation, northeast–southwest rather than the conventional east–west: the original pre-Christian structures on the site would have been aligned in this way so they would face the sunrise at the summer solstice.
This Saxon doorway was reset in the north aisle, built in 1885.
Although the timber church would have existed at the time of the Domesday survey in 1086, it was not recorded in it; only the village was. The absence of church records from the survey was common, though, as its main purpose was to record landholdings for taxation purposes. By this time, a stone-built Saxon church would have been in place; Ralph de Cahaignes possibly ordered its construction to replace the old wooden building. After the Norman conquest, many Sussex churches were rebuilt in Norman style, although Saxon fabric was sometimes retained, and this happened at Horsted Keynes. One doorway and the foot of the tower survive from the Saxon era; the doorway has been repositioned in the north aisle.
This pointed arch is all that remains of the 14th-century former chantry
From left to right, the north aisle, west end of the nave, southwest porch and south transept are visible.
In place of the Saxon building, the Normans constructed a large cruciform church with a central tower and tall, sharp spire which forms a landmark for miles around despite the church standing in a dip. The four arms of the cross were formed by the nave, the chancel and a north and south transept. The chancel had an apse and a narrow chancel arch. In about 1220 (the Early English Gothic architectural period) many changes were made. The apse was removed and the chancel was completely rebuilt with a square end and a longer floorplan. Lancet windows were installed, including a large triple window in the new east end. The south transept was also reconstructed and given lancets. The old transept must have been smaller and lower, more like a porch, because the low original 12th-century arches leading to the crossing were retained.
The tower is topped with a landmark spire.
More changes took place in the early 14th century, by which time English Gothic architecture had moved into its Decorated Gothic phase. A new wider chancel arch was installed between the crossing and the chancel, a side chapel was added on the north side, new windows were added in the nave, and the original rounded west arch of the crossing (into the nave) was replaced by a new pointed arch. The side chapel probably replaced the old north transept, which was removed "for some reason unknown"; its roofline can still be traced. All of this work apparently took place between 1320 and 1330. One contemporary feature that has now disappeared was a chantry chapel dedicated to Marie de Bradehurst. It was built alongside the chancel and was latterly used as a schoolroom until it was removed in the Victorian era. The dedication relates to the Broadhurst manor in Horsted Keynes parish. The demolition of the chapel revealed the outline of a wide blocked pointed arch on the south wall, which is still clearly visible.
Later work included reconstructing the porch at the southwest corner—dated to the late 17th century—and reinforcing the tower and the west walls of the nave, necessitated by the subsidence of the tower caused by the removal in the 14th century of its north transept and its original rounded west arch. The tower started to lean, and its tall spire accentuated the problem. Buttresses were added in four places, and iron ties were inserted later to bring the tower back towards the vertical. The spire is known to have been in place by 1667, when lightning struck it and dislodged 3,000 shingles.[note 3]
Victorian restoration was carried out at the church, as at many ancient churches in Sussex. Spencer Slingsby Stallwood, a Reading-based architect, was commissioned to carry out his only work at a Sussex church at St Giles' in 1885, in association with his colleague Joseph Morris. The work may have continued until 1888, and involved the construction of a north aisle and arcade, the replacement of the 18th-century king post roof, and some improvements to the north chapel, apparently instead of an earlier scheme (announced in 1840) to rebuild the demolished north transept. The old king post roof had been installed in 1714. Changes inside included the removal of old box pews and a wooden gallery at the west end, which had latterly been used by church musicians. The work cost £2,300. The Saxon doorway, which was once believed to be a "Devil's door", was inserted in the new north aisle during this work. More restoration was carried out between 1959 and 1960 or 1961 by Brighton architect John Leopold Denman's firm Denman & Son; his work revealed traces of an old Norman window in the nave.
For many years the church was a peculier of the Archbishop of Canterbury rather than being held by the Bishop of Chichester, head of the local diocese. It was also one of about 20 churches in the area covered by the diocese at which the ancient Law of Sanctuary applied.