A word of thanks to all of those who have collaborated in the realization of these pages, in particular we would like to mention:

Mauro Agnesoni, Carlo Aldinucci, Massimiliano Angelini, Francesco Barbagli, Duccio Gazzei, Carlo Guerrini, Luca Nardi, Giacomo Paciotti, Simone Pagni, Leonardo Rossi, Andrea Valeriani, Ermanno Vigni.

The English version was translated by Michael Kucher.

We give special thanks to the Comune of Siena and University of Washington  for hosting us on their web servers.