BARCELONA, Spain (AP) — A blackout brought much of Spain and Portugal to a standstill Monday, halting subway trains, cutting phone service and shutting down traffic lights and ATM machines for the 50 million people who live across the Iberian Peninsula.

Power has been restored to tens of millions of people across almost all of Spain and Portugal, but disruptions to transport services were expected to stretch into a second day as questions mount over what caused a massive blackout.