Musée de l'Armée audio guide,
five stops, free.

Stand close to the glass and let your eyes adjust. The metal is black, not polished silver, and the black is the point. It is iron that has been deliberately darkened, then inlaid with silver and gold in lines of scrolling foliage that run down every plate in parallel. Black and silver were the personal colours of the man it was made for, Henri d'Orléans, second son of King François the First.

He was not supposed to inherit anything. In 1536 his elder brother François died a few days after a game of tennis, with rumours of poisoning flying at once, and Henri, at seventeen, became the Dauphin, the heir to France. This armour was made for him in that in-between decade. Look for a crown anywhere in the decoration and you will not find one. That absence is how the museum dates it: after 1536, when he became heir, and before 1547, when he became king.

Now find the monogram. An H for Henri is interlaced with a C for his wife, Catherine de' Medici. Look again and the same shape reads as a D. D for Diane de Poitiers, the older woman the museum politely calls the prince's favourite. The bow and quiver worked into the decoration, the attributes of the huntress Diana, point the same way.

There are dolphins too, in facing pairs. The French word for dolphin is dauphin, and the heir's title came from the same word, so the fish are a pun on the wearer. Three interlaced crescent moons repeat across the plates, an emblem the Valois family favoured.

The whole suit stands 1.75 metres and weighs 19.7 kilos. That weight matters. Parade armour is thin and light because nobody strikes it. This is heavy enough to fight in, which is why the museum calls it war armour. It came from Milan, from the Negroli family of armourers. Filippo Negroli and Francesco Negroli, who specialised in exactly this silver inlay, called damascening, probably shared the work.

It sat in the French Crown's collections until 1797, passed through the national library in the Revolution, and reached the artillery museum, this museum's ancestor, in 1872.

Henri became king in 1547 and reigned twelve years. In the summer of 1559, at a tournament held to celebrate a peace treaty, a lance splinter from Gabriel de Montgomery, the captain of his own Scottish Guard, wounded him, and the great surgeon Ambroise Paré could not save him. He died ten days later. The suit in front of you was built for the battlefield. The wound that killed the man it was built for came from the tournament ground.

He is looking straight at you, and almost nothing else in the picture moves. Ingres has set the Emperor dead centre, face on, symmetrical, with a golden laurel wreath on his head and two long rods framing him like a pair of brackets. In his right hand is a sceptre topped with a tiny statuette of Charlemagne. In his left, the hand of Justice. At his side, a sword modelled on Joyeuse, Charlemagne's legendary blade. The purple velvet robe is sewn with golden bees, the Empire's chosen emblem alongside the eagle. This is the costume Napoleon wore for his coronation at Notre-Dame on the second of December 1804, and Ingres painted it two years later, aged twenty-six.

Everyone hated it. Shown at the Salon of 1806 as number 272, the painting was called Gothic and barbarous. The critics were unanimous, and Jacques-Louis David, then finishing his own enormous Coronation, judged it severely. What upset them is what makes it strange now: the frontal pose that turns a living man into an idol, the head emerging from a mass of fur and velvet like a face in a Byzantine icon, or Jupiter on his throne. The art historian Robert Rosenblum thought Ingres had borrowed the pose from Van Eyck's God the Father on the Ghent Altarpiece, which was hanging in the Louvre at the time.

Look at the top right corner. A shield is cut off by the edge of the canvas. It carries the arms of the kingdom of Italy, which is why the museum thinks the painting was meant to be sent to Italy, to show Napoleon as its king. The historian Sébastien Allard suggests the Italian commissioners refused it, and that is how it came to belong to the French legislature instead.

Now crouch a little and look at the carpet. Along its left border, among medallions of the zodiac, Ingres has slipped in a small version of Raphael's Madonna della seggiola. He worshipped Raphael and hid tributes to him in painting after painting. Here the tribute sits under the Emperor's feet.

The canvas is two metres sixty high. It belonged to the Legislative Assembly until 1814, passed to the royal museums, and in 1832 it was sent here to the Invalides, hung first in the chapel and from 1860 in the library. The Louvre still carries it on its inventory as number 5420. The portrait that Paris laughed at in 1806 is now, by the museum's own reckoning, one of the most famous images of Napoleon there is.

You are looking down at him. That is how the architect built it. Louis Visconti cut a circular crypt into the floor under the dome, open to the church above, so that anyone who comes to see Napoleon has to lean over the balustrade and bow their head to do it. Take the stairs down and the sarcophagus towers over you instead.

The stone is the first thing everyone asks about. It is not porphyry, whatever the older guidebooks say. It is red quartzite from a quarry in Karelia that belonged to Tsar Nicholas the First of Russia, standing on a base of green granite from the Vosges. Inside it are six coffins, one inside the next, and inside the sixth is the Emperor.

He should not be here at all. Napoleon died on Saint Helena in 1821 and was buried there. In 1840 King Louis-Philippe decided to bring him home, and on the fifteenth of December that year the coffin arrived under this dome and was placed in the Saint-Jérôme chapel to wait. It waited a long time. Visconti had to dig out the centre of a seventeenth-century church to make the crypt, and he died in December 1853 with the work unfinished. The body was finally laid in the sarcophagus on the second of April 1861, more than twenty years after it came back to Paris.

The building itself is older than any of this. Jules Hardouin-Mansart built it from 1677 as the royal chapel of the Invalides, the home for old soldiers that Louis the Fourteenth founded, and its gilded dome was the tallest thing in Paris until the Eiffel Tower. During the Revolution it became a temple of the god Mars. In 1800 Napoleon himself had the tomb of Turenne, Louis the Fourteenth's great general, moved here and declared the church a pantheon of military glory. Vauban followed a few years later. Napoleon was choosing the company he would keep.

Look around the gallery that circles the crypt. Twelve pillars, and between them relief panels celebrating what the Emperor did, with sculpture by Pradier, Simart and Duret. Then think about who else lies in the building: his brothers Joseph and Jérôme, his son Napoleon the Second, the Eaglet, his generals Bertrand and Duroc, and the marshals of a later war, Foch and Lyautey.

One story from the building's darkest years. In the Second World War the occupying army made the Invalides a barracks. The Morin family, who lived on the premises, hid Allied airmen here, under the noses of the garrison, for three years.

And the stone he was first buried under on Saint Helena came back with him in 1840. It stands a short walk from here in the cour de Nîmes, a garden along the Saint-Louis church: a plain gravestone from an island in the South Atlantic, a few hundred steps from all this red stone.