Boston Is One of the Best Prepared U.S. Cities to Handle a Crisis

Witnesses repeatedly described the scene Monday at the finish line of the Boston Marathon, where two bomb blasts ripped through a crowd of spectators, as unimaginable. Security experts called Friday's citywide "shelter-in-place" order unprecedented, and onlookers could only compare the siege in Watertown, where soldiers, SWAT teams, helicopters and armored Humvees cordoned off a large swath of the neighborhood, to a movie.

But emergency management personnel in the Boston region had not only been imagining such a complex scenario, they had been rehearsing it.