The object is about 54 by 35 by 29 centimetres, the horse hollow-cast, the whole thing produced by the lost-wax method. The disc is roughly 25 centimetres across and is not a single plate: two bronze discs joined by an outer ring, with a thin sheet of gold laid over one face. Punches and gravers filled both sides with concentric circles and bands of zig-zags, and the gilded face carries an extra outer zone that may represent rays, plus a ring of looping bands that - in one of the better descriptions of Bronze Age ornament - instead of flowing one way, progress like the steps of a dance, twice forward and once back. Only one side is gold. That asymmetry is the whole point.

Read the object as a diagram and it says this: the sun is hauled across the sky from east to west through the day, showing its bright face to the earth, and returns west to east through the night, showing its dark one. The horse pulls it in the direction the gilding faces - the right-hand side, viewed from behind the horse. Danish work on rock carvings and on the decorated bronze razors of about 1100 to 500 BC fills in the rest of the crew: a fish brings the sun to a morning ship, the ship carries it to midday, the sun horse takes over for the afternoon, a snake leads it down into the underworld at dusk, and a night ship returns it to the fish at dawn. The cycle holds forever, provided everyone does their part.

Here is the detail that gives the object away as equipment rather than illustration. On the rock carvings and the razors, the horse draws the sun on a line - there are no wheels in the story at all. The wheels on the Trundholm piece were added so that a person could roll the sun back and forth, west and east, bright side and dark side, reproducing the sun's journey with their own hands. This was not a statue on a shelf. It was a thing to be pushed along a floor or a ground surface, in ceremonies whose content nobody has recovered, by people demonstrating to each other how the sky worked.

The chariot was already damaged in the Bronze Age. It was very likely put into the bog deliberately, as an offering, and Danish wetlands took in a great deal of valuable metal on those terms over the following centuries. Whoever gave it up was not discarding it. In 1998 a metal detector at the same spot brought up further fragments of the six wheels, still lying where they had been left. The dating puts the piece around 1400 BC - Montelius period II, roughly 1500 to 1300 BC, with the National Museum favouring about 1350. Wheeled vehicles were not new to the region by then: petroglyphs, chariot bits and whip handles show horse-drawn chariots in Scandinavia from around 1700 BC.

Two discs from Ireland belong to the same conversation: the Lattoon gold disc, and the bronze Cooke disc of about 1500 to 1300 BC, whose fittings resemble Trundholm's closely enough to suggest it too once sat on wheels behind a sun horse. The Nebra sky disc from central Germany, made in the same broad era, is another node in the same network of sky-watching. Some scholars go further with Trundholm - the archaeologist Christoph Sommerfeld has argued that the ornament on both faces numerically encodes the nineteen-year Metonic cycle, a reading also proposed for the later Berlin Gold Hat. That claim is contested, and reading numbers out of prehistoric decoration is treacherous. What is not in doubt is simpler and grander: some time around 1400 BC, in Odsherred, people modelled the daily motion of the sun in bronze and gold and made it go.