The glory of St Mary's Church, Ewelme, is a magnificent alabaster monument to Alice de la Pole, Duchess of Suffolk. Richly carved, painted and gilded, it commemorates the church's patron who died in 1475 at the age of 71.

Diminutive, gold-winged angels bear up the cushioned head of the sleeping duchess who wears the Order of the Garter. This was an exceptionally rare honour for a woman, and created some puzzles about protocol.

After all, genteel Ladies of the Order could hardly wear the Garter on the thigh. Reportedly, Queen Victoria sent to Ewelme church before her coronation to discover the correct way to display the decoration. She was, no doubt, reassured to learn that Alice de la Pole wore the Garter on her left forearm.

A quiet village of venerable red brick, Ewelme stands on a rise of the Chilterns some four miles north east of Wallingford. Its hillside, surmounted by mediaeval church, almshouse and school, descends to a picturesque duckpond and a chalk stream that runs through the village and was once famed for its watercress beds.

Commercial growing made Ewelme Cress!' a once familiar cry at London's Covent Garden Market. Production ceased in 1988 and with neglect, the stream's flight of low, wooden dams began to disintegrate. Later, however, local villagers contacted the Chiltern Society for help. The site was purchased to restore the watercress beds, with their wildlife haunts of heron and kingfisher, and a visitor centre opened in 2004.

In conserving tradition, the people of Ewelme have a notable forebear in a 17th-century soldier named Colonel Francis Martyn. His aim, however, was not to preserve the natural habitat but the treasures of Ewelme church.

After the English Civil War, when Roundhead zealots were smashing and desecrating religious ornaments throughout the country, Colonel Martyn commanded Cromwell's army in the district.

A Ewelme man, he stood in front of the church door brandishing his sword to deter any soldier from entering, also ensuring that no harm came to the rector.

The saviour of St Mary's, who died in 1682, is commemorated in a handsome memorial set high on the north side of the chancel.

The church's star attraction, though, is the tomb of duchess Alice, a monument created in three tiers. Below the serene, recumbent figure of the noblewoman is the chest containing her remains.

At the lowest level, enclosed by an arcade, is the effigy of an emaciated corpse clothed in a shroud, representing the duchess in death. Here is an alternative take on mortality, and you have to stoop to make out the macabre figure. The mediaeval craftsmen did not shrink from confronting the stark realities of human decay, however exalted by glittering visions of transcendence.

Alice was the granddaughter of the poet Geoffrey Chaucer, and one of the greatest ladies of her day. During the 1430s she and her husband, William de la Pole, rebuilt the existing church, incorporating only a part of the earlier tower.

Next to her own tomb is that of her father Thomas Chaucer, Lord of the Manor of of Ewelme, Constable of Wallingford Castle and Speaker of the House of Commons. By tradition the author of the Canterbury Tales often stayed at Ewelme with his son and daughter-in-law.

Thomas and his wife, Matilda, are commemorated in fine brasses, and their tomb's sides are embellished with a sumptuous display of coloured shields of arms. With a background in the wool trade, the de la Poles were the first great noble English family to have risen from the merchant classes and were clearly not to be outshone by anyone.

The fabric of the church is much as it was in the time of the de la Poles. The two great tomb memorials stand south of the chancel, in the Chapel of St John. Its timber roof is exquisitely carved with angels bearing shields at the intersections of the beams, and the east window contains pieces of stained glass which date from the time of building. In the chancel itself, the octagonal stone font is also contemporary with the church. The amazing font cover, stacked with narrowing tiers of wooden arches, rises to more than 10 ft in height, with a pulley and counter-weight to raise it. Above, supporting the roof, stone corbels bear grotesque carved faces that look down with varying expressions of mirth and unease.

Outside, the church's brickwork battlements are striking and, at the east end, a chequer pattern of squared stones and flints also surprises the eye. The style is unusual for Oxfordshire but less so in parts of East Anglia where the Duke of Suffolk had his chief estates.

At Ewelme he lived with Alice in a palatial mansion where Henry VIII and Catherine Howard were to spend their honeymoon. It later fell to ruin, though the present Georgian manor house retains some vestiges of the building. The ghost of Duchess Alice was once reported by the village school mistress, who saw a tall lady veiled in black emerge from the manor gates before disappearing.

If the mansion has gone, other architectural legacies of the de la Poles survive. Besides building the Church of St Mary, Alice and William also founded the adjoining almshouse and school.

A covered passage leads from the church's west door into the almshouse cloister, a delectable retreat whose little gabled houses are grouped around a square courtyard, bright with flowers at the time of my visit.

License for the almshouse was granted by Henry VI on 3 July 1437, and Statutes provided for two chaplains and 13 poor men to be maintained. In mediaeval times the needy inhabitants wore cloaks with a red cross on the breast. Though the uniform is no longer a requirement, almsmen are still cared for at the site to this day, with a resident nurse attending to their needs.

The school, a doughty, two-story block of mediaeval brickwork, is buttressed by two massive chimneybreasts and ornamented with carved figures bearing shields. The building, probably completed around 1450, has been schooling local children for well over 500 years.

Its statutes provided that the pupils should be taught freely without exaccion of any Schole hire' and it remains a source of pride that it is the oldest Church of England school still to be using its original building. Part of the present day state system, it has never been used for private education but still serves the children of the village.

Almshouse and school both speak of a remarkable continuity in the spirit of Christian charity. We know much about the cruelties of mediaeval life; at Ewelme we are reminded of mediaeval kindliness.

The Church of St Mary at Ewelme is open daily, all-year-round, services permitting.