Life in Spain and Portugal began to return to normal Tuesday, a day after a massive power outage paralyzed the Iberian Peninsula, leaving governments, companies and experts scrambling to figure out what went wrong.

Electricity was back in most of the two countries almost 18 hours after a blackout that shut down much of daily life. The cause of the outage remained unclear.

A massive power cut hit large parts of Spain and Portugal on Monday, causing widespread chaos and disruption. The outage left millions of people without electricity, while internet and phone networks were also down. Trains were cancelled and evacuated in some regions, traffic lights stopped working amid mounting delays at airports.