The country’s top officials were trying to determine the cause of an outage that left tens of millions of people across the Iberian Peninsula without power.

Lights flickered back to life in Spain and Portugal on Tuesday after a massive blackout affected almost 90 percent of the Iberian Peninsula. According to AFP, barely a corner of the peninsula, which has a joint population of almost 60 million people, escaped the blackout which began on Monday.

One of Europe’s most severe blackouts grounded flights, paralyzed metro systems, disrupted mobile communications and shut down ATMs across the Iberian Peninsula.