Turkey's accession to the European Union would not only bring a huge Muslim population into the EU, but would extend its boundaries deep into the Caucasus mountains and down towards the plains of ancient Mesopotamia.
Turkey - a bridge between East and West?
The EU would have borders with Syria, Iraq, Iran, Georgia and Armenia.
For some this would be a good thing. Turkey was once the "sick man of Europe" as its empire began to decay and other powers circled around, fighting each other, as in Crimea.
Turkey as a bridge
Now it would be a link between East and West, between a continent with a Christian history and a land of Muslim faith in which both would respect religion, but not rely on religion to determine the course of government.
It would extend the ties developed with Turkey through Nato into the more fundamental ties of political association.
It would build on the strong secular nature of Turkish public life forged by the great Kemal Ataturk, who fought the British at Gallipoli before leaving a legacy of modernism influential to this day.
Turkey's acceptance, it is felt, would erase the centuries of conflict in which the Ottoman Empire sought to stretch its hand into Europe and where memories of battles against the Turk still linger.
The EU, after all, is designed not to forget history but to overcome it.
The siege of Vienna
Only recently was one such battle, the siege of Vienna in 1683, invoked by a European commissioner to argue against Turkish entry.
"The liberation of 1683 would have been in vain," declared Dutch commissioner Frits Bolkenstein.
In that siege, it was the Polish King Jan Sobieski who led a force which drove the Turks away. How appropriate, those favouring Turkish entry now argue, that Catholic Poland and Muslim Turkey might one day join together in the Union.
How much more compelling would be a final rapprochement between Greece and Turkey - and a settlement in Cyprus which would obviously have to be part of any accession agreement.
An enlargement too far?
For others, Turkey would be an enlargement too far. Turkey is not really a European country, they argue, despite its foothold on the European continent across the Bosphorus.
Its population, already 69 million, is second only to that of Germany, which has 82m. But projections for Turkey's people go up and for Germany's go down so that by mid-century, Turkey would probably have the largest population in the EU.
That population, it is further argued, would be mainly Muslim and despite the influence of the secular Ataturk, the influence of the fervent Enver Pasha might one day prevail.
Enver Pasha, one of the "Young Turks" who overthrew the remnants of the Ottoman sultanate, had a vision of extending Turkish and Muslim rule to the peoples of the Caucasus. During World War I, he threw his lot in with the central powers of Germany and Austria and attacked the Russians during a winter campaign, which proved disastrous.
The Armenian people of eastern Turkey were force-marched south and west, in one of the earliest examples of ethnic cleansing in the 20th Century.
But it is not the past as much as the future which worries some modern European governments.
One basic rule of the EU is the free movement of goods and people. The prospect of millions of poor Anatolians flooding into the EU is one which easily raises European concerns. Restrictions on such movement for some years might well form part of accession conditions.
The third view
There is a third view - that accession talks might not even lead to Turkish membership.
John Palmer, political director of the European Policy Centre in Brussels, said: "It is certain that the EU will set a date for negotiations with Turkey at the summit in December.
"The reforms are sufficient for talks, but not yet sufficient for membership. They will be unusual talks. Both sides agree that it will be 15 to 20 years before a decision is required. In my opinion, Turkey will not worry about the time. What matters is that the process of Turkish transformation is linked to the process of negotiation.
"The separate question is whether at the end of this, there will be a yes decision by both sides. I do not think that there is a pre-ordained outcome to that."
Turkey will force the EU to debate what it is and what it wants to be.
I first became aware that Turkey might not be a welcome member of the European club in 1984, when Claude Cheysson, who had just ended a spell as French foreign minister, asked a group of British correspondents over an excellent dinner in Strasbourg: "Is Turkey European?"
Being an accomplished diplomat, he had avoided giving a direct reply about Turkish membership and accompanied his own question with a shrug of the shoulders and a quizzical smile. Turkey was something to be left for another year - or century. We moved on to the cheese.
His question has not yet been fully answered.