An official report into Italy's national power blackout has criticised Swiss authorities for not reacting quickly enough as the crisis unfolded.
The blackouts brought Italy to a standstill
The Union for the Co-ordination of Transmission of Electricity (Ucte) said the blackout occurred after two separate lines carrying power from Switzerland into Italy shut down after being hit by trees during a storm.
This overloaded all other power lines into Italy, triggering the collapse in supplies.
The official report said the blackout could have been avoided if staff at the Swiss Electricity Co-ordination Centre (Etrans) had taken more effective action in the 30 minutes between the two power-line failures.
The September blackout in Italy left more than 50 million people - almost the entire country's population - without power for up to 18 hours.
COUNTDOWN TO BLACKOUT
0301: Tree hits Mettlen-Lavorgo line
0311: Etrans calls Rome power centre of Italian grid operator GRTN to lower power imports
0321: GRTN's lower power imports comes into effect
0325: Sils-Soazza line also tripped after it is hit by tree
0330: Power blackout hits Italy
The report said the sequence of events began when a tree hit a Swiss line during a storm in the early hours of 28 September.
Because the remaining lines had higher-than-normal loads, an automatic device aimed at protecting the equipment blocked attempts to put the line back into service.
Etrans, based in Laufenburg, Switzerland, called the Rome-based control centre of Italian grid operator GRTN 10 minutes later and asked it to lower imports of electricity to relieve the overload in Switzerland.
GTRN complied within 10 minutes, but that still took the total time for the power overload to 20 minutes - five minutes longer than the time allowed for problems to be resolved.
So when a second line was hit by a tree around 30 minutes after the original incident, overloads on remaining lines became "intolerable", setting off a chain of events which culminated in plunging the entire country into blackness.
UCTE criticised the Swiss response to the first power cut as "insufficient" and lacking a sense of urgency".
However Etrans said in a statement quoted by the Associated Press news agency the UCTE report ignored "grave weaknesses" in Italy's handling of its own network and "focuses one-sidedly on the events in Switzerland".
It also said that, while it had made available all necessary information, Italians failed to provide voice recordings.
The power cuts followed similar ones in the United States, Canada, the UK, Denmark and Sweden.