As Tamburlaine asked, is it not passing brave to be a King and ride in triumph through Persepolis? Had Marlowe seen for himself the glories of that fabled capital, he could, perhaps, have dwelt further on the riches of ancient Persia: the vast bas-reliefs of warriors and horsemen ornamenting the palaces and staircases, the elaborate stone pillars, lions of lapis lazuli (pictured), gold and silver drinking bowls, reliefs depicting the procession of subjects — delegates of an empire that stretched from India to Libya — bearing gifts to King Darius, and exquisite bracelets, torcs and gilded amphora handles in the form of a winged ibex.

At its height, the empire created by Cyrus and ruled in subsequent splendour by Darius and Xerxes covered most of the known world. It reached a level of sophistication, artistry and innovation barely equalled by Rome almost a millennium later: the first postal system, a global currency, a tax and communications system, a canal linking the Nile and the Red Sea, a federal administration that relied on local governors known as satraps, religious tolerance and, above all, equine prowess and mastery.

How much of all this do we, the distant beneficiaries, now remember? Alas, very little. The Persian empire lasted a mere two centuries, from 550-330BC. It ended in catastrophe, when Alexander of Macedon burnt Persepolis and smashed the imperial system.

And, thanks to Thermopylae, Marathon and Thucydides, we have seen the titanic struggle between Persians and Greeks only through the eyes of Persia’s enemy. But even a century ago more was known of this ancient realm than now: the British Museum, from earliest days, began amassing relics, bracelets and jewellery from the far-flung provinces once ruled by Persia. Many came from a huge cache found in the 19th century, known as the “Oxus Treasure”.

Now, augmented by holdings from the Louvre and an unpredented loan from Iran, it has put these treasures together in a magnificent new exhibition: Forgotten Empire: The World of Ancient Persia.

The sweep of glory is there, including much that has never been outside Iran or even on public display before. There are painted tiles and artefacts from the palaces, as well as delicate vessels and objects from the royal dining tables. One room displays the workings of the postal system on the long road from Susa to Sardis. There are clay tablets with details of ancient divorce settlements or messages from Jewish soldiers serving in the army. A wonderful mastiff stands guard with a patina of polished stone as gleaming now as 2,500 years ago. The luxury in life and death as well as the influence and objects from Greece are shown, and, famously, the world’s first declaration of human rights: the iconic Cyrus Cylinder, which records his decree allowing the Jews to return home from Babylonian captivity.

Four years in planning, the exhibition has overcome political tensions and the uncertainties of Iran’s elections to present one of the finest depictions of an ancient civilisation of which we have seen too little. It is well worth seeing it now.

Box office: 020-7323 8181