Spain has recovered more than 92% of its power following an unprecedented blackout that brought much of Spain and Portugal to a standstill, officials said.

Spain and Portugal were returning to some semblance of normality early Tuesday, with many questions remaining about what caused one of Europe’s worst blackouts in years across the Iberian peninsula the previous day.

An unprecedented blackout brought much of Spain and Portugal to a standstill on Monday, stopping trains, cutting phone service and shutting down traffic lights and ATMs for millions of people across the Iberian Peninsula.