How did the Elgin Marbles get here?
A sculpture from the Elgin Marbles has been allowed to leave the UK for the first time since Lord Elgin turned up in Greece in early 1800 and had them stripped from the Parthenon and shipped to Britain.
"Elgin believed he was rescuing the sculptures from the risk of further damage," writes Neil MacGregor, director of the British Museum, in The Times on Friday.
Athens' Parthenon, a classical temple built by the ancient Greeks, was in a dilapidated state by the time Thomas Bruce, the seventh Earl of Elgin, became British Ambassador to the Ottoman Empire in 1799.
Partially destroyed by early Christians, converted into a mosque and later used as a weapons store by the Ottoman Turks, some 40% of the Parthenon's 2,250-year-old sculptures had been destroyed by the time Elgin took up his diplomatic post in Constantinople.
Elgin, an art lover, claimed the sculptures were better off in Britain than the perilous environment he found them in.
In 1801, he negotiated what he claimed was permission from the Turks - who then controlled Athens - to remove statues from the Parthenon.
The document upon which Elgin claimed legality has been cited by campaigners on both sides of the argument, whose interpretations of it inevitably differ.
The British Museum maintains that Elgin was an official diplomat and had acted with the permission of Turkish authorities.
Greek campaigners argue that the Turks were a foreign force acting against the will of the people they had invaded.
The opposing sides agree on only one thing - that the Elgin Marbles form one of the most important collections of classical art in existence.
The Marbles which were taken to Britain include about a half (some 75 metres) of the sculpted frieze that once ran all round the building, plus 17 life-sized marble figures from its gable ends (or pediments) and 15 of the 92 metopes, or sculpted panels, originally displayed high up above its columns.
Plundering classical art was common practice in that era, which saw those on the Grand Tour regularly pilfer "souvenirs" from ancient sites.
Fragments from the Parthenon alone ended up in some 10 European countries, or were lost altogether.
On his return to England, Elgin told a Parliamentary inquest that a desire to protect what was left of the treasure was part of his motivation in taking them. The Turks, he claimed, had been even grinding down the statues to make mortar.
However, in prising out some of the pieces that still remained in place, Elgin's agents inevitably inflicted further damage on the fragile ruin.
The argument attributed to Elgin that the Marbles could be admired by people from all over the world in their new location is also contradicted by his original intention to house them in his private home.
The sculptures were transported to Britain between 1801 and 1805; by 1807 they were on show in London.
For Elgin, at least, the triumph was short-lived.
Bankrupted by the acquisition and in the throes of a humiliating divorce from his wealthy wife, Elgin needed cash.
So began a new chapter of the history of the Marbles - as museum objects.
In 1816, Parliament paid £350,000 for the Parthenon Marbles - most of which went to Elgin's many creditors - and a new home was found at the British Museum, albeit initially in a shed.
Since 1832 - apart from the years when they were sheltered in Aldwych underground station to avoid war damage - the Marbles have remained in the British Museum.
A highlight of the British tourist trail, their uncomfortable acquisition has put them at the heart of one of Europe's most entrenched cultural disputes.
In a blog about the loan, Mr MacGregor said the British Museum was a "museum of the world, for the world".
The arrival of the Elgin Marbles in London, it is argued, transformed Europe's understanding of ancient Greek Art.
"They are integral to the whole idea of the Universal Museum and the way museums over the last two centuries have come to display and interpret human culture," writes Professor Mary Beard.
It was first argued they should be returned to Greece in 1925, and today Greece still refuses to recognise the Museum's ownership.
Thirty per cent of the remaining sculptures remain in Athens, which the Greek authorities maintain is their proper home and natural cultural landscape.
"It's time to heal the wounds of the monument with the return of the marbles which belong to it," said then Greek President Karolos Papoulias in 2009, at the opening of the Acropolis Museum.
But so far British authorities have opposed all calls for the return of the marbles, with David Cameron saying last year that he did not believe in what he called "returnism".