Italo Calvino's book "Invisible cities" gives the name to this collaborative etwinning project among Spain, Czech Republic, Italy and Norway. 

The project was developed in two phases: Mathematics to travel to the (in)visible cities (2013) and eTwinauts in the (in)visible cities (2013-2014). 

 

The (in)visible cities are presented as a set of travel stories that Marco Polo tells to Kublai Khan, the emperor of the Tartars. 

Italo Calvino says that a book is a space which the reader must enter, wander round, maybe lose his way in, and then eventually find an exit, or perhaps even several exits, or maybe a way of breaking out on his own*.

We pretended not to write a book but to develop a project in which all of us, teachers and students, were going to enter, wander round, maybe lose our way in, find an exit, perhaps several exits or maybe a way of breaking out on our own... 

 

The result is a journey to discover the wonderful things, the visible and invisible part of a set of cities which are included in UNESCO heritage list. We started the adventure discovering the secrets of Brno, Prague, Telc, Z'Dar nad Sázavou, Lednice, Český Krumlov, Madrid, Barcelona, ​​Santiago de Compostela, Valencia, Toledo, Granada and our journey continued to a well known landmark of barter goods as it is the port of Bergen, to the memories of industrial paternalism in Crespi d'Adda, to the Roman Empire in Segovia, to the desire of transform an Italian industrial town in Manhattan, to the traces of the musical language in Litomyšl and to the signs from the language of Mathematics, Physics , Chemistry and artistic and literary expression in all of them.

 

Marco Polo describes a bridge, stone by stone.
"But which is the stone that supports the bridge?" 
Kublai Khan asks.
  "The bridge is not supported by one stone or another," Marco answers,   
"but by the line of the arch that they form."
Kublai Khan remains silent, reflecting.
Then he adds: 
"Why do you speak to me of the stones? 
It is only the arch that matters to me."
Polo answers: 
"Without stones there is no arch.”

(Italo Calvino, Invisible cities)

 

*Lecture given by Italo Calvino to the students of the Graduate Writing Division at Columbia University on March 29, 1983.