Outside Umberto Eco's office window in Milan looms the intimidating mass of Sforzesco castle, a reminder, with its towers and black birds, of various continental wars. Here once stood the 14th-century Castrum Portae Jovis – the Porta di Giove fortress – which was destroyed by the short-lived Aurea Republic of 1447. Between these walls, Leonardo Da Vinci and Donato Bramante once laboured; these very buttresses were conquered by Napoleon. And just beyond the moat – an area now invaded by tourists who have come to visit Michelangelo's La Pietà Rondanini – Marshall Radetzky's Austrian troops bombarded the rioting city in 1848.

"When it comes to the debt crisis," says Eco, "and I'm speaking as someone who doesn't understand anything about the economy, we must remember that it is culture, not war, that cements our [European] identity. The French, the Italians, the Germans, the Spanish and the English have spent centuries killing each other. Today, we've been at peace for 70 years and no one realises how amazing that is any more. Indeed, the very idea of a war between Spain and France, or Italy and Germany, provokes hilarity. The United States needed a civil war to unite properly. I hope that culture and the [European] market will do the same for us."

Eco sips his coffee, preferring suitably postmodern Nespresso capsules, whereas his German wife, Renate Ramge Eco, defends the traditional Italian coffee pot, the moka. He has just returned to Milan from Paris, where the French president, Nicolas Sarkozy, conferred on him the rank of commander, the third rank of the Legion of Honour.

"Those were the hours of France's battle for the AAA rating, but Sarkozy still didn't want to miss it – great. I must admit it was also a moving experience when I was conferred the Dodecaneso Cross in Greece: they hand them out right inside Patmos cave, where St John wrote the Apocalypse," says the writer, with a laugh.

"One of the advantages of living in Europe is that I get birthday greetings from the German president, Wulff, and the Spanish prime minister, Rajoy, neither of whom I know. After being at each other's throats for years in fratricidal wars, we're now all culturally European."

Asked to describe European identity in 2012, Eco says it is widespread but "shallow". "I am using an English word that is not the same as the Italian word superficiale, but which is somewhere between 'surface' and 'deep'. We must change this, before the crisis strips it [Europe] of everything.

"The university exchange programme Erasmus is barely mentioned in the business sections of newspapers, yet Erasmus has created the first generation of young Europeans. I call it a sexual revolution: a young Catalan man meets a Flemish girl – they fall in love, they get married and they become European, as do their children. The Erasmus idea should be compulsory – not just for students, but also for taxi drivers, plumbers and other workers. By this, I mean they need to spend time in other countries within the European Union; they should integrate."

It's an attractive idea, and yet pride in Europe appears to be giving way to populism and hostility within the union. "That's why I said that our [European] identity is 'shallow'. The founding fathers of Europe – Adenauer, De Gasperi and Monnet – may have travelled less. De Gasperi spoke only German because he was born within the Austro-Hungarian empire and didn't have access to the internet to read the foreign press. Their Europe reacted to war and they shared resources to build peace. Now we must work towards building a more profound identity.

"When I proposed at a meeting of EU mayors the idea of also introducing Erasmus for craftsmen and professionals, a Welsh mayor said: 'My citizens would never accept this!' And when I spoke about this a few days ago on English television, I was slapped down by the anchorman, who was worried about the euro crisis, about a supranational Europe and about the technical governments of Papademos in Greece and Monti in Italy who were not 'elected', and are therefore 'undemocratic'.

"How should I have responded? By saying that ours is a government approved by parliament and proposed by a president elected by parliament? By saying that in all democracies there are unelected institutions, such as the Queen of England, and the American supreme court, but that no one defines them as non-democratic?"

Even before the debt crisis, Europe's weak identity – as diagnosed by Eco – was apparant. "[For instance,] when the constitution was rejected in a referendum. The document had been written by politicians; it was impossible for any educated man to participate in the process and it was never discussed with voters. It was also evident when euro banknotes were designed without the usual faces of important men and women – instead, there were just frigid landscapes, as in a De Chirico landscape. Or does the problem [of European identity] go back to God - the fact that the United States becomes ever more religious as Europe becomes even less religious?

"That's the way it is. Back when Pope Wojtyla was still alive, there was much discussion on whether they should accept the European constitution and the continent's Christian roots. Secular people predominated and they did nothing about it. The church protested. There was however a third way, more difficult, but one that would give us strength today.

And that would have been to speak of the constitution of all our roots – the Greek-Roman, the Judaic and the Christian. In our past, we have both Venus and the crucifix, the Bible and Nordic mythology, which we remember with Christmas trees, or with the many festivals of St Lucy, St Nicolas and Santa Claus. Europe is a continent that was able to fuse many identities, and yet not confuse them.

That is precisely how I see its future. As for religion: be careful. Many people who no longer go to church end up falling prey to supersitition. And many who are non-practising still carry around a little saint card with a picture of Padre Pio in their wallets!"

Father of semiology, scholar of mass culture, author of essays for the elite and global bestsellers – from The Name of the Rose to The Prague Cemetery, Eco has just turned 80. Whenever he gets tired climbing a flight of stairs, he jokes: "Eh, my friend, we're not 70 any more!"

He is no pessimist: "With all of its defects, the global market makes war less likely, even between the USA and China. Europe will never be the United States of Europe, a single country with a common language like the USA – where for a long time English was threatened to be overtaken by German, now overtaken by Spanish.

"We have too many languages and cultures, indeed, the idea of an unique [European] newspaper is for now just a utopia. The web, meanwhile, makes us bump into one another; we may not read Russian but we come across Russian websites and we are made aware of others.

"I still think that there is no longer a disparity between Lisbon and Warsaw, just as there is no disparity between San Francisco and New York. We will remain a federation, but indissoluble."

So whose faces should we print on our banknotes, to remind the world that we are not merely 'shallow' Europeans, but profound? "Perhaps not politicians or the leaders who have divided us – not Cavour or Radetzky, but men of culture who have united us, from Dante to Shakespeare, from Balzac to Rossellini.

"And since Pierre Bayard is right, we know there are books we have yet to read that will help us reflect on cultures different from our own. Little by little: that is how our European identity will become more profound."