Gales blazed across the Alpine region as usual during autumn. In the early morning of September 28, 2003 a severe storm forced a tree to sway near the Italian-Swiss border. Unfortunately, the branches tripped a power line. The load of the disturbed line is automatically divided among other cables. These transmission lines were already utilized close to their full capacity. To relieve them from excessive load, the Italian transmission network operator (TSO) decided to cut down electricity imports by 300 MW. Twenty-four minutes later another tree hit a high voltage line. This second incident overloaded remaining transmission lines between Italy and Switzerland. In order to contain the problem, Italy was isolated from the European grid of the Union for Coordination of Transportation of Electricity (UCTE) – encompassing the cooperation between 23 European TSOs.

This separation from the UCTE network caused a frequency instability in Italy, which eventually led to the collapse of the domestic system.1 Less than two minutes after Italy's isolation from the European interconnected network the entire Italian peninsula was deprived of electrical power. The largest blackout in Italian history was a fact. All over the country trains came to a halt and traffic lights went off. In Rome, where the annual all-night festival Notte Bianca was taking place, plunged into darkness. The Roman subway system came to halt, trapping thousands of passengers. The Vatican put backup generators into action, enabling the pope to proclaim new cardinals on early Sunday morning. An ongoing liver transplant had to be aborted and postponed in a Trieste hospital. Only after half a day the whole of Italy was once again supplied. The blackout not only disrupted Italian society, but also led to the death of at least four people.

The UCTE immediately appointed a committee to evaluate the blackout. Not awaiting the report, various actors began to search for the roots of the blackout, and initially pointed fingers at each other across the Alps. An Italian newspaper reported how Swiss and French authorities blamed Italy for not handling the crisis properly. In response, the Italian TSO claimed that their inability to restore control over the system was not the root of the blackout.