A cross-border power blackout on Monday paralysed the Iberian Peninsula for most of the day, disrupting millions of lives across Spain and Portugal – even interrupting the French electrical system. The sweeping power outage that hit Spain and Portugal this week has raised questions about the electricity grid in a region not normally known for blackouts.

The massive power outage on the Iberian Peninsula has cost at least three lives. The search for the cause of the outage continues.

Red Eléctrica, Spain’s electricity grid operator, ruled out a cyberattack, human error or unusual weather. Experts say it could take weeks to determine the cause.