The oldest part of our church is the part near the entrance door, the west end of the north aisle – thought to have been built during the first half of the 12th century or earlier. The south wall of this 12th century church is built on Roman foundations. Roman tiles and artefacts have been found under the floor. A large Roman wall runs below ground level parallel to the north wall. The eastern part of the north aisle (now the Chapel of the Nativity) and the tower were built during the second half of the 12th century. During the early 13th century the original wooden roof was replaced by stone vaulting. Frescos dating from this time can be seen on the east of the roof vaulting. They depict (i) ‘Les Trois Rois Morts et les Trois Rois Vifs’, (ii) a martyr wearing a black habit carrying a chalice in his left hand and a flagon in his right with an axe laid across his neck, and (iii) The Last Supper. The frescos can be lit by rotating clockwise a time switch near the organ. In the same area, the south east pillar supporting the tower is pierced by a hagioscope (a squint/peep hole, perhaps used by a priest at a chantry altar to keep watch on celebration at the High Altar).
The church was enlarged to the south, it is thought during the second half of the 14th century, by the present chancel and nave, columns and arches piercing the original south wall. About this time the spire was added to the tower. To the left of the present High Altar (south east corner of the church) there is a blocked priest’s door and to the right a piscina. The floor level was altered in the 1870s to elevate the new altar, leaving at ground level a cupboard, thought to have been for storing altar vessels. A furnace used to recast the bells of the church was discovered toward the west end of the south aisle, when the church floor was renewed in 1878. The bell casting pit and parts of the clay mould dated 1680 bearing the fleur-de-lys mark of the Normandy bell-founder were found during floor works near the same area in 1999.
Changes to the shape and appearance are evident from the outside. Look at the windows, the oldest have square lintels. The west window above the entrance porch is one of the few remaining l8th century sash windows in a Channel lsland church.
Looking closely at the outside walls you will see altered windows, blocked doorways, re-used Roman bricks and stonework, and a sundial set high on the south western corner of the church. The Neolithic (or early bronze age) statue menhir, set near the main door probably dates between 2500 and 1800 BC. In front of the statue are the stone seats used by the former medieval court of Fief St Michael. Former standing stones were re-used in the foundations of the new 12th and 14th century building, and broken pieces Christianised with an incised cross may be seen in the north and south entrances to the churchyard. Set in the wall of the church porch you will see a fireplace lintel reputed to be from an earlier fifteenth century rectory; its inscription reads ‘Orate pro eo’ (Pray for him) and the central lozenge contains the letters ‘T’ ‘H’ (for Thomas Henry, Rector, died 1494). Outside the west end of the church, south of the porch, stands a late 13th or 14th century sink (now used as a plant trough) with lion and leopard heads identical to those ordered for Edward I in the Palace of Westminster in the 1280s.
Church registers date from 1674 and are now stored in the Priaulx Library in St Peter Port. The list of Rectors of the parish dating from 1262 reveals the changes in life and worship. Until the latter part of the 16th century Castel Church followed Roman Catholic teaching and practice. Then followed, in common with the rest of the Island, a period of French Calvinistic influence and appointment of a Calvinist Rector in 1584. In 1662 King Charles II ordered the Book of Common Prayer and the practice of the Church of England to be followed. The first Anglican Rector was appointed in that year, and ever since Sainte Marie du Castel has been a church of the Anglican Communion.