On a brisk winter day, Stephen Puleo, author of Dark Tide: The Great Boston Molasses Flood of 1919, gestured towards the spot where a tank in Boston's North End burst, releasing a tsunami of hot molasses into the streets 100 years ago, on January 15, 1919.

"So, that green sign right there is exactly the site of the outside wall of the tank. Ships that would come up from Puerto Rico, Cuba, and the West Indies would pull up right along here. There was a pipe right here that led to the molasses tank, and they would offload gallons of molasses into the tank."