An unprecedented blackout brought much of Spain and Portugal to a standstill Monday, stranding thousands of train passengers and leaving millions of people without phone and internet coverage and access to cash from ATMs across the Iberian Peninsula.

It is rare to have such a widespread outage across the Iberian Peninsula, with a combined population of about 60 million people. Spain’s Canary Islands, Balearic Islands and the territories of Ceuta and Melilla, located across the Mediterranean in Africa, were not affected.

Electricity returned to much of Spain and Portugal a day after a blackout affected critical infrastructure. The cause of the outage remained unclear.