East Anglian Treasures: Ian Collins considers the magnificence of the churches of the Fens and Marshland.

By turns strange, sinister and exhilarating, the Fens form a flat geometric grid plotted on a monumental scale. Long straight lines of roads and dykes cutting through enormous fields look from an aerial view like one vast Mondrian painting.

Since an engineer called Vermuyden crossed from Holland in the 17th century to start draining what was then a swathe of marshy sea, a Dutch connection has been confirmed repeatedly. For here is a highly fertile plain and our own piece of polder country.

No skies are bigger than those looming above this epic construction – a land of obliterated borders where Lincolnshire, Norfolk and Cambridgeshire meet and merge.

Indeed, the sky seems literally to be pressing down on reclaimed earth as oxidised soil sinks ever further below sea level. And as the North Sea rises, the expulsion of water starts to look like a temporary triumph.

Windmills have given way to windfarms, but what point most firmly heavenwards (and even appear to hold back the sky in places) are the stone fingers of spiritual creations.

While the medieval masterpieces of Ely and Peterborough cathedrals and ruined Crowland Abbey loom largest, a score of church towers seem to be stretching out – growing taller and taller as if through an elemental tug-of-war.

This visual miracle (or optical illusion) has attracted artists from John Sell Cotman to John Piper. The latter, jolted out of abstraction by fear that Britain's architectural glories had to be recorded before being lost to bombs or bulldozers, returned again and again to our fragile flatlands in a near-50-year creative journey.

In paint and print he waxed lyrical over marvels of the Middle Ages raised on tiny mounds above the waters between Wisbech, King's Lynn and the Wash – the churches at West Walton, Walsoken, Walpole St Peter (deemed by collaborator Sir

John Betjeman to be the finest in England), the Tilneys, Terringtons and Wiggenhalls. All were built by masons 'using majestically the Fens as a plinth – the best plinth for sculptural architecture in the whole country'.

As early as 1940 Piper was writing in the Architectural Review: 'From a distance their upright outlines are straight enough, but straight and upright with an unaccountable richness.

Closer, they are seen to have dissolved away around their stratified core of stone as if they had been under water or had been sand-blasted by a vague and artistic mechanic.'

Serrations in the surface of each block had become as deep as the gaps made in the joints by the wind, frost and rain, making the substance of every wall a sculptural whole. 'It is incised and pitted by the weather; lichen stars or spreads it with yellow and gold; the mouldings of windows and arcades have become encrustations of curving ribs,' Piper continued.

Such was oneness of the churches in relation to the landscape that the artist thought it 'fanciful but suggestive to imagine that these towers have been carved out of the level Fens, and the whole area of the land around them reduced in height by a hundred feet or so, leaving them solid and whole, like some Indian rock-temples'.

Accordingly, his Turneresque oils and watercolours portray these structures as more impressive in mass than in detail, ideally viewed from a low angle and against a backdrop of dazzling colour and a dramatic interplay of light and shadow.

Piper concluded: 'Grey and gold and brown, and sometimes none of these, the towers are always afloat on a sea of Fengreen. Changeable skies give them bodies of infinitely varying light, sometimes pale and almost white against heavy clouds and shadowed marsh, sometimes burnished, sometimes glimmering, sometimes vivid, sometimes dim.'

From such sweeping grandeur we may then hone in on glorious detail – such as the angel roof at March. Or else we may rest our senses in the plainness of Guyhirn Chapel – built for diehard Puritans in 1660, the year Cromwell's Commonwealth gave way to restored monarchy.

But neither the returning Stuarts nor the restoring Victorians were to alter such levelling austerity.

After surveying the church at Upwell, Dorothy L Sayers gave her thriller The Nine Tailors a Fenland setting – an atmosphere of menace amplified in Graham Swift's novel Waterland.

Miraculous and murderous, the Fens are a mysterious sea in which ancient stone ships still sail.