Firefighters investigating what they've described as the biggest blaze in Boston in decades say it was caused by some men setting off fireworks from the roof of a nearby building.

Fire department Lt. Hank Sheridan said Tuesday the men caused the fireworks to travel to a vacant warehouse, igniting its roof. The resulting blaze brought in about 170 firefighters from across the city.

The fire was reported Saturday night in the Roxbury neighborhood and wasn't completely out until Sunday afternoon. It destroyed the warehouse and caused $750,000 in damage. No one was hurt.

The cause of the fire was determined after investigators examined physical evidence, interviewed witnesses and reviewed burn patterns.

The fire has been ruled accidental. But the culprits may be cited for illegal activity.