THE Cathedral, the Palatine Chapel that abuts the Royal Palace, the exquisitely decorated Abbey of Monreale - these are living evidence that Palermo in Sicily in the 12th century was one of most richly endowed capitals of Europe.

It is there, amid this splendour, that the Polish composer Karol Szymanowski and his cousin and librettist Jarosjław Iwaszkiewicz set their masterpiece Król Roger (King Roger), an opera that evokes the magnificence of this civilisation where the paths of Crusaders crossed, while Roman, Norman, Byzantine, and Muslim flourished, freely intermingling under a firm but enlightened regime.

Sketched and composed in 1918-24, King Roger was brought, at last, to the Royal Opera House this month, in a production by Kaspar Holten, its current Director of Opera, that captured its tensions and desolation powerfully.

Gone were the gold mosaics and regal splendour; they were replaced by a sparer vision by the designer Steffen Aarfing, Holten's fellow Dane. His modernist interpretation made almost as massive an impact: a huge, skull-like bald head, initially bathed in gold and orange-red, which echoed rather ominously the look of the Byzantine Pantocrator (God as all-creator), and which as Act 2 approaches was swung round to reveal a complex of stairways, patterns, and levels that suggested the inner workings of the mind.

But whose mind? The central figure in the opera is one of medieval Europe's great enlightened Christian monarchs, Roger II of Sicily. In the first Act, resplendent with Byzantine chant sung by a chorus trained to perfection by Renato Balsadonna, we see him at mass in Palermo Cathedral, confident and irresistible, upholding the traditions of the Church and seeking its endorsement.

Into the heart of the service breaks the voice of the young Shepherd (the Albanian tenor Saimir Pirgu), who brazenly challenges the community to abandon its creed and embrace a new, liberated religion. His effect is disastrous: the initially hostile populace is prised away from its traditional dogma, while Queen Roxana (the American soprano Georgia Jarman) is attracted to the new creed, and the King is left floundering between suppressing this renegade cult, or legitimising it and becoming an avid follower.

Sinuous unclad figures writhe around the beleaguered monarch, underlining parallels with Euripides' late Greek play The Bacchae, on which King Roger is partially founded, where wild oriental dancers invade Thebes and the young King begins to find not just his rule but his sexuality questioned.

Though Roger in history was a strong king, in this fantasy we find him a bit of a wet, unable to consummate his marriage, and strangely drawn to this beckoning outsider. His ambiguous position causes him to put his realm at risk.

There were drawbacks. I didn't find many of the moves helped especially: Roger (Mariusz Kwiecień) was never established or endowed with enough power or stature, so that neither his near-demise nor his final hymn to the sun (beautifully sung) achieved the impact one looked for. Some re- fined moments verged on the shambolic. Importantly, Roger's minister Edrisi (the splendid tenor Kim Begley) should be close to the King, present, advising and warning, as in a concert performance; all too often here he was physically removed.

The performer who was most skilfully, lithely moved was the enraptured Roxana, a touching figure whose plaintive, Arab-influenced cantilena or vocalise was gorgeously and meltingly sung.

At the opera's end, the original plan was that Roger should yield to his temptations and follow his wife in paying homage to this alien cult. In Nietzschean terms, he would be embracing his Dionysiac side, and making peace with his subterranean yearnings.

But Szymanowski chose to amend the final Act, so that instead, after a night of mayhem, Roger turns, isolated and lonely, to welcome the sunrise, thus opening himself to the benign, enlightened influence of Apollo. The wild shenanigans have made him the wiser, but have not claimed him.

Besides the baritone Kwiecień, who received a massive ovation as the King, the biggest triumph of all was the Orchestra of the Royal Opera House, who - whether in massive build-ups (as in the cathedral), wildly cavorting scherzo (the Shepherd's followers' orgiastic dance), or the subtlest of individual touches - yearning solo violin, harps, celesta, expressive woodwind, and some vital brass, sometimes muted - produced a wonderful array of sounds under the direction of Sir Antonio Pappano.

A full performance can be viewed on the Royal Opera House website, YouTube, and the new Opera Europa Digital Platform, www.theoperaplatform.eu