New York City on Monday marked 20 years since a massive blackout plunged the five boroughs — and much of the eastern seaboard — into darkness. 

The Northeast blackout of 2003 shut off power to much of the region, as well as parts of the Midwest and Canada. 

About 50 million people were left in the dark.

Traffic lights went out, the subway system was shut down and passengers were stranded at airports.

The outage was believed to have stemmed from a series of faults caused by tree branches touching power lines in Ohio, along with human error, software issues and equipment failures.