"It looks idyllic!" said a tourist from Melbourne in Australia as she admired the harmonious mix of palazzi, churches and immaculately-kept homes of Pienza, a town of 2,000 people in the Italian region of Tuscany.

"I think it's nice to live in a town like this because the food is grown very close to where you're living," said Kay, part of the growing number of visitors coming to view a town set apart from the usual tourist routes.

Ochre-coloured Pienza is structured around a spectacular piazza and was designed to be as pleasant to live in as possible and to blend with nature.

It overlooks the fields and vineyards of the Val d'Orcia – a picturesque backdrop that has been registered as a UNESCO World Heritage site.

The town was commissioned by a pope, Pius II, a native son who was born into a local aristocratic family in what was then the village of Corsignano.

The finest architects of the time and some 20,000 workers took part in the construction, which took just three years between 1459 and 1462.

Pius II, born Enea Silvio Piccolomini, was an unusual figure viewed from a contemporary perspective. A cleric steeped in humanist learning and the author of poetry, sociological treatises and even an erotic novel.

The pope dreamt of a Renaissance city, a humanistic city," Vittorio Carnesecchi, curator of the papal palace, Palazzo Piccolomini, told AFP in an interview.

"Pienza was born from the dream of a great humanist who recruited the greatest engineers of his time to realize this utopian city," he said.

It was named "Pienza" ("Pius Town") in his honour.

Manlio Sodi, who comes from near Pienza and teaches at the Salesian Catholic university in Rome, said the urban landscape he created could be seen as "the fruit of the cultural horizons of the Piccolomini pope".

The style of the main cathedral is Gothic, similar to the churches in Germany that the pope had visited during extensive travels which also took him to England, France, Scotland and Switzerland.

The result of his varied tastes was "a cultural fusion between northern and southern Europe" in the architecture of Pienza, Sodi said.

"It is an amazing synthesis that was part of his objective of peace among nations," Sodi said.

Pienza was the first "ideal city" ever realized – and has been followed by many examples through the ages from the Brazilian capital Brasilia to the utopian urbanism of French-Swiss architect Le Corbusier.

The town has been kept pristine largely thanks to contributions from the Piccolomini family through the centuries and an enlightened urban administration.

But Sodi said the idea of building a similar "utopian city" would be too difficult because the lack of a "common idea" in society of what it should look like.

"At the time, papal authority was sufficient for resolving a lot of things. Today I believe it would be unthinkable to create an ideal city," he said.