Thorvaldsen, like so many painters and sculptors coming to Italy from dour, northern European Protestant countries, found moral and sexual release in Rome. The passage of time has also revealed Thorvaldsen's own eccentricities and peculiarities He seems a very various artist. The men and women whom he immortalised in bust form look less like togaed Romans or vestal virginsand now are betrayed by their coiffures as distinctly 19th-century creatures. The nascent democracy naturally sought cultural symbols of its new-found sense of identity - and Thorvaldsen's gentle, bloodless, classical, implicitly republican art was perfectly adapted to the purpose.These days, Thorvaldsen's classicism tends to look a little less classically perfect than it did 150 years ago. The museum was opened, some years after his death, in 1848, a year of bloody revolutions in Europe but one of bloodless constitutional reform in Denmark - it was the year that quietly sealed the Danish nation's rejection of monarchical absolutism and its embrace of democracy (when the delegation from the Danish Parliament finally went to King Ferdinand VII to demand reform, early one morning, he is said to have muttered, "So, at last they have come - tell them yes, of course they may have reform", and to have gone straight back to sleep). The outside of Thorvaldsens Museum boasts a painted frieze depicting the artist's triumphant return to Denmark with all his works.

Here we see delegations of politician and bureaucrat kneeling gratefully before the conquering hero on the Copenhagen quayside. Thorvaldsen, the master of a neo-classical sculpture tradition that was itself on its last legs, had been canny enough to suspect that coming home was his only chance of immortality. He did so, following many entreaties and on the sole condition that a museum be built to him and all his works, which he consented to leave to the nation. Thorvaldsen, after all, was a Danish artist who spent almost all his creative life abroad, and whose aesthetic rested precisely on the rejection of Denmark and the embrace of Italy. But nations take artists to their hearts for many and often somewhat peculiar reasons and Thorvaldsen is clearly a prime case of the phenomenon.He was blessed by historical circumstance and shrewd enough to recognise the fact. The opera is musically unexceptional and may, to non-Danish speakers, seem a little boring. But it has been exceptionally well attended by large and good- humoured crowds of Danes who are still, evidently, happy to consider Thorvaldsen as a national institution.There is something of a paradox here.

In 1998, yet larger celebrations will mark the 150th anniversary of the opening of Thorvaldsens Museum. This year, when Copenhagen is the European Union's designated City of Culture, they have been getting in some practice, with talks, lectures and frequent performances of a chamber opera based on the sculptor's uneasy relationships with women and connoisseurs. Here, in stone relief, Priam pleads pathetically with Achilles for Hector's body, Cupid revives the swooning Psyche, and a Jason who looks suspiciously like Michelangelo's David ponders, with calm, impassive self-satisfaction, his recent acquisition of the Golden Fleece.There is something touching about the Danish nation's fidelity to a man who, had he been born French or Italian (or British), would certainly have been allowed to slide quietly into the oblivion of art historical footnote status. Next year, which sees the bicentenary of the sculptor's so-called "Roman birthday" - 8 March, 1797, the day when Thorvaldsen first entered the Eternal City and, as he said, "the ice melted" from his eyes - will be marked with due solemnity.

In Denmark, it seems no opportunity to remember Thorvaldsen's former pre-eminence goes unmissed. It is a wonderful museum, a work of art in itself and a building characterised by an entirely unique combination of the grandiose and the quaint. Within the building, in the echoing halls and atriums devised in homage to Thorvaldsen's classical spirit by the architect MS Bindeboll, they strive to keep the flame of Thorvaldsen's memory alight. Here, in rooms of burnt sienna, cobalt blue and sunflower yellow, they preserve the memory of a moment in European art when it seemed that the great, classical subjects were indeed the only subjects for art.