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.

MADRID (AP) — The cause of Spain and Portugal’s widespread blackouts remained a mystery on Tuesday, with some isolated disruption remaining after power was largely restored to both countries.