Ten years ago today, Toronto suffered a power blackout.

Streetcars ground to a halt, traffic lights ceased to function, and the entire city was transported back to the days before electricity. Then reports began to come in that it wasn’t just Toronto. It was the entire province, and several US states.

As to what caused it, there was immediate finger-pointing on both sides of the border. The culprit ended up being a tree branch that touched a power line in Ohio, plunging 50 million people into the dark.

Mel Lastman was mayor of Toronto at the time. He says that the 2003 blackout brought out the best in the people of Toronto. Despite concerns that the blackout would leave homes and business vulnerable to looting, there was no spike in crime. Some people even filled in for the darkened traffic signals, keeping traffic flowing through the blacked-out streets.

Power executives say they have learned from the Blackout of 2003 and the likelihood of such an event occurring today is low. But they say Ontario is still vulnerable to faults in other power systems joined to our grid.