Spain suffered several power glitches and industry officials sounded repeated warnings about the instability of its power grid in the build up to its catastrophic blackout on Monday.

A massive and unprecedented power outage on Monday hit large parts of Spain as well as Portugal. The blackout halted subway and railway trains, cut phone service and shut down traffic lights and ATMs for the millions of people who live across Europe's Iberian Peninsula.

It was the second serious European power outage in less than six weeks after a March 20 fire shut down Heathrow Airport in the U.K.