Place names are among the most durable things a culture produces. Thorsager keeps a Norse god in it, and the reasonable inference - the one Danish scholarship draws - is that the site mattered religiously before Christianity arrived on Djursland. It is speculation that the hill itself was regarded as sacred, and it is worth flagging as speculation. The physical evidence is narrower and more interesting: under the present church lay the traces of a timber predecessor, built in the tenth or eleventh century. So the sequence at Thorsager runs old belief, wooden church, brick church, each occupying the same ground. That layering is common across Scandinavia, but rarely is it labelled so plainly by the address.

Thorsager Church went up around the year 1200, in Romanesque brick, and it is the most recent of Denmark's seven surviving round churches - the last word in a form that was already going out of fashion. Who ordered it is not settled. Records show King Valdemar II held Torsager and its holdings in 1231, valued at a hundred marks of gold, but the likelier patron is Bishop Peder Vognsen, who knew buildings of this kind. Its ground plan matches the former church at Schlamersdorf in Wagria, on the Baltic coast of what is now Germany, and Danish architectural historians group it with Bjernede and Horne as one of the so-called Absalon round churches. Tower, round nave and apse are all brick - munkesten, the big medieval monk's brick that gives Danish churches their particular warm red.

Step inside and the geometry does something no rectangular nave can. The round nave is roofed with small ribless cross vaults, and a spiral staircase winds around it up to a low-ceilinged room above the vaulting. That loft, and the tower over it, rest on four heavy brick pillars planted in the middle of the floor. Danish round churches were built with upper storeys that could serve as refuge in unsettled times, and Thorsager's loft belongs to that tradition - though it sees almost no use now, because the staircase reaching it is narrow enough to be a serious hazard if anything ever caught fire. During the Middle Ages a second tower and a church porch were added on the western side; the tower would not survive the nineteenth century.

In 1877 the Royal Building Inspector of Jutland, Vilhelm Theodor Walther, began three years of work on the church, guided by the confident nineteenth-century instinct to return a building to its original state and disregard everything the intervening centuries had added. He took down the medieval western tower. Outside, generations of whitewash had left the old bricks weathered and cracked, so most were swapped for machine-made replacements; the original brickwork now survives only on the north side of the nave. Inside, he plastered the walls white and painted them with frescoes. The result looked much like the church of 1200 and felt nothing like a building that had been used for seven hundred years. Between 1950 and 1952 nearly all of it was reversed - plaster and frescoes stripped, brick whitewashed instead, new altar, pulpit and floor installed, pews replaced with individual chairs.

The oldest object in the church is the medieval baptismal font, fitted with an eighteenth-century basin. The brick altar dates only to 1952, but the altarpiece above it is a late Gothic crucifix from the fifteenth century inscribed I mig skal I have fred - in me you shall have peace. Light comes through a panel of stained glass made by the artist Harald Borre in 1955, showing the resurrection. A bible published under Christian VI in 1740 rests on the altar; the candlesticks are seventeenth century, the chalice from 1878, the pyx from 1965. The most recent changes came in 2004, when the interior was whitewashed again, the pulpit gave way to a lectern by the local artist Birger Holmgaard Johansen, and the 1909 organ was replaced by a fifteen-register instrument from Bruno Christensen & Sønner. That last decision paid off in an unexpected way. The dome over the round nave turns out to be superb for music, and concerts here are well attended.