Electricity is pulsing through Spain and Portugal again after a massive outage knocked out power in both countries on Monday. So too are questions.

The hunt has begun for the cause of a massive blackout across Spain, Portugal and parts of France that halted trains, bank machines and traffic lights, in one of Europe's biggest ever power system collapses.

Spain, Portugal and other parts of Europe are hit with widespread power blackouts which lasted 10 hours in Lisbon, Portugal on April 28, 2025. Cellphone networks were cut off and many people were left stranded at airports. (Photo by Stringer/Anadolu via Getty Images)