  We describe the road which led to the construction and exploitation of
electron positron colliders, hightlighting how the young physics student Bruno
Touschek met the Norwegian engineer Rolf Wideroe in Germany, during WWII, and
collaborated in building the 15 MeV betatron, a secret project directed by
Wideroe and financed by the Ministry of Aviation of the Reich. This is how
Bruno Touschek learnt the science of making particle accelerators and was
ready, many years later, to propose and build AdA, the first electron positron
collider, in Frascati, Italy, in 1960. We shall then see how AdA was brought
from Frascati to Orsay, in France. Taking advantage of the Orsay Linear
Accelerator as injector, the Franco-Italian team was able to prove that
collisions had taken place, opening the way to the use of particle colliders as
a mean to explore high energy physics.
