Will the built-up area ever stop? Will it go all the way to the Balkans, Greece and Italy?
Perhaps it will, especially if Turkey becomes a member of the European Union, and also because Istanbul, with a population of who knows exactly how many millions of people, is one of the world's fastest growing cities, expanding north, south, east and west.
But what I could not help thinking, as I made my way to Lake Buyukcekmece on the far side of the city's Ataturk Airport, is that the Ottoman Empire that drove Istanbul for the best part of half a millennium, once headed this way too.
If Suleiman the Magnificent, the 16th Century Ottoman emperor, had had his way, the road west would have led directly to Rome - the city that had been the hub of the empire that had created Istanbul, or Constantinople, in the first place.
Calling himself "Caesar of all the lands of Rome", Suleiman dreamed of reconnecting Istanbul with Rome.
He would do it by conquest, travelling on the road that passes over Lake Buyukcekmece on a bridge designed and built by his architect, Sinan.
In fact, his armies did set foot and hoof in Italy - but they never made it as far as Rome.
In recent years the superb bridge, too narrow for modern traffic has been bypassed.
A lonely tourist attraction, it takes off from a sorry-looking public park, complete with a cartoon-style statue of Sinan sporting an ambitious turban, and lands at the foot of another concrete panorama, blocking the view west.
This was the bridge Suleiman saw rising as he set off on his last military adventure, to conquer Hungary. He was killed in the campaign so never saw it completed.
Nor had he managed to forge a direct link between what had been the ancient Roman Empire and his New Rome, Ottoman Istanbul.
From his death in 1566, the empire sank into a long, if exquisite, decline.
Yet one legacy Suleiman left is that of his architect, Sinan.
Sinan lived to be 100, realising hundreds of designs for mosques and madrassas, bridges and aqueducts.
This contemporary of Michelangelo and Andrea Palladio, two of the most influential Italian architects, is little known in the West, yet not only did Sinan shape some of the world's finest buildings - who could argue with the choice of his Suleymaniye Mosque in Istanbul or Selimiye Mosque in Edirne? - but his work was also to influence that of the most ambitious architects of the Italian Renaissance, as theirs was to affect his.
What I came to understand on my latest trip to Istanbul - with the penny, or Turkish Lira, dropping as I walked across Sinan's Buyukcekmece bridge - is just how real this connection was.
Istanbul was joined to the West culturally if not politically or in terms of religious belief, and if not by political treatises, then by architecture.
Michelangelo's dome, soaring above the roof of St Peter's, Rome, was surely influenced by those of Sinan's daring mosques in Istanbul.
Equally, it seems possible that Sinan would have seen drawings by the Italians.
Palladio's champion and patron, Marcantonio Barbaro, was for six years the Venetian ambassador to Istanbul.
Surely he made some sort of connection between Sinan and Palladio?
Whenever I go to Venice and look afresh at Palladio's sublime churches of St Giorgio Maggiore and Il Redentore - the Redeemer - I am sure I am seeing or scenting something in their design from east of the Mediterranean - from Istanbul?
Somewhere in undocumented Ottoman archives, scholars might yet stumble on correspondence between the greatest architects of Italy and Istanbul, confirming a connection between the Italian and Suleiman's Renaissance, between the old and new Romes.
The desperate sprawl of modern Istanbul makes today's city somehow further from Rome, the West or the European Union, than Sinan and Suleiman's city was 500 years ago.
As I stood on the haunting bridge across Lake Buyukcekmece it seemed somehow sad that the road across it leads not to some new glory or to a shaking of modern Turkish hands in western Europe, but to the blank-faced and all too solid walls of yet another, architecture-free concrete housing estate.
Source: news.bbc.co.uk, Saturday, 13 February 2010