Hofburg audio guide,
five stops, free.

Stand in the square with the Kohlmarkt at your back and look south-west. The curved white front ahead of you, with a green copper dome over the gateway, is the Michaelertrakt, the side of the Hofburg that faces the old city. The drawing is from 1726. The building is from the 1890s.

Joseph Emanuel Fischer von Erlach designed this front in the reign of Charles the Sixth: a sweeping curve that would carve a proper square out of what was then just a crossroads. Work began around 1730, the Winter Riding School end on your left was finished, the round hall behind the gate was half built, and then the emperor died and nothing more happened. From 1742 Maria Theresa's court theatre, a converted ballhouse, stood in the gap, and it stayed there for almost a century and a half. Only when the new Burgtheater on the Ring was ready in 1888 could the old one come down. The court architect Ferdinand Kirschner then built Fischer's plan, lightly altered, between 1889 and 1893, and the wing opened on the eighth of September 1893.

Now compare the two domes. Fischer's engraved design showed no domes at all. The low dark one on the left sits on the old riding-school end; the architect Carl von Hasenauer argued that a low side dome demanded a raised one in the middle, and Kirschner had to give way. The operator puts that central dome at fifty metres.

Then drop your eyes to the ground floor. Either side of the three gates stand four groups of Hercules, each cut from a single twenty-five-tonne block of stone: Hercules killing the Hydra, freeing Hesione, unchaining Prometheus, and hauling Cerberus up from the underworld. They were made to match an older set of Hercules groups inside the courtyard. In the curved pavilions at either end are two great wall fountains. On the left, Power at Sea by Rudolf Weyr, signed on the ship's bow: WEYR 1895. The Neptune in it is said to have the face of Friedrich Uhl, editor of the Wiener Zeitung, who was also the sculptor's father-in-law. On the right, Power on Land by Edmund Hellmer, unveiled two years later, and unsigned.

Two more surprises. This design was built long before Vienna got it: in Berlin, between 1775 and 1780, Frederick the Great had it used for his Royal Library. And under the middle of the square lie the remains of four Roman houses from the second to the fifth century, part of the civilian settlement outside the legionary camp of Vindobona. The palace wing in front of you had to be founded sixteen metres deep.

You are in In der Burg, the inner courtyard. The red and grey gate on its south-east side is the oldest face the Hofburg shows you. Stand back by the bridge railings and look at it square on.

Behind that plain wall is the core of the medieval castle, the Alte Burg. Its four corner towers are gone, and most of its moat and the drawbridge went too, but not here. When Ferdinand the First rebuilt this entrance wing between 1551 and 1554, he kept the ditch and gave his new gate a drawbridge, on purpose: a portal modelled on a Roman triumphal arch that still behaved like a fortress. The lifting gear was still recorded in 1770. The railings stand on the masonry bridge that replaced it.

The gate dates from 1552, the year spelled out at the end of the inscription: M D L I I. Read the gilded letters either side of the crowned arms and you have Ferdinand's titles: king of the Romans, of Germany, Hungary and Bohemia, Infante of Spain, Archduke of Austria, Duke of Burgundy. Three of those letters are not old. The N in Germany, and the R in Hungary and in Austria, were only put back in the restoration of 1949. The colours are not the first ones either. The gate began in blue-grey, gold and red; at some point between 1763 and 1830 it was painted red and grey, in 1853 plain grey, and in 1927 red and grey again, which is what you see now. The man paid for the painting in the sixteenth century was Pietro Ferrabosco, who spent forty years building fortresses and palaces for the Habsburgs.

The name is younger: it comes from the Swiss Guard, who kept watch here from 1745 to 1767.

If you walk into the passage, look up at the painted vault, with the arms of Austria, Styria, Carniola, Carinthia and Upper Austria. Then look low on the base of the inner arch, about seventy centimetres up, for a line of Latin dated 1660: if God is for us, who can be against us. Legend says Leopold the First scratched it there himself. Beyond lies the Schweizerhof, with the palace chapel of 1449 and the Imperial Treasury, keeper of the regalia of the Holy Roman Empire.

Now turn to your left, to the north-east side of the courtyard. That long front with the Kaisertor in its centre, Lorenzo Mattielli's Labours of Hercules on its portals and the shield of Charles the Sixth rising from its roof edge is the Imperial Chancellery Wing. The Hercules groups on Michaelerplatz were made to match these. And behind those windows is where Franz Joseph lived.

Out on Ballhausplatz, walk south onto the great open square, Heldenplatz, and stop by the rider nearer the Volksgarten. Look at the horse before the man, because the point of this statue is underneath it.

The horse is rearing, and it stands on its two hind legs alone. For a bronze of this size that is a feat of balance, and Anton Dominik Fernkorn, sculptor and bronze founder, managed it exactly once. Look across the square at the other rider, Prince Eugene: there the horse's tail comes down to touch the pedestal. Fernkorn could not repeat the trick. By the time Prince Eugene was unveiled in 1865, illness had ended his working life and his pupils had finished it for him, and a popular view at the time held that the failure itself had broken him.

The man on this horse is Archduke Charles, who beat Napoleon at Aspern on the twenty-first and twenty-second of May 1809. The pose, flag in hand, is modelled on a famous painting by Johann Peter Krafft. Fernkorn made a bronze model in 1847, Franz Joseph confirmed the commission in 1853, and the statue was cast in eight pieces. Read the plaques on the pedestal. The words are by Theodor von Karajan, approved in 1858 on the recommendation of the poet Grillparzer. The dedication says 1859, because the unveiling was planned for the fiftieth anniversary of Aspern. Then came the military setbacks in northern Italy that year, and the ceremony was put off until the twenty-second of May 1860.

Now turn to the south-east. The great curved wing with its colonnade is the Neue Burg, finished in 1913, one half of an imperial forum that was never completed. Its twin was meant to rise on the Volksgarten side, and never did. That gap is why, if you turn north-west, the square stays open to the Ring, with the Parliament, the City Hall and the Burgtheater in view. It was from the balcony of the Neue Burg that Adolf Hitler proclaimed the Anschluss of Austria to the crowd on this square, on the fifteenth of March 1938.

To the south stands the Outer Castle Gate, put up in 1824 in honour of the veterans of the Napoleonic Wars, and rebuilt as a war memorial in 1933 and 1934.

The square only took its name, Heldenplatz, the Heroes' Square, in 1878, from the two commanders on horseback. Before you go, look up at this one once more: eight pieces of bronze, one field marshal, and all of it resting on two hind legs.