It was one of seven paintings that were commissioned from different artists at the same time, to hang in the militia companies' hall, the Kloveniersdoelen.
The militia companies formed a civic guard which combined the jobs of firemen, police officers, and the military; they put out fires, guarded the city gates, quelled disturbances, and represented the city at state ceremonies.
The Netherlands was a relatively new state which had just won its liberty from the Spanish, so there is also a patriotic significance to the subject.
Though the painting is always known as The Night Watch, that title arose as a misunderstanding because of the intense darkening of the original varnish. Its official title is more accurate and informative, but less memorable: The Militia Company of District II under the Command of Captain Frans Banninck Cocq and Lieutenant Willem van Ruytenburch.
While other painters working on similar commissions ranked the musketeers in rows facing the front, like a school photograph, Rembrandt took a uniquely dramatic approach.
This is not a formal portrait but a scene from an action movie. Everything is happening at once; one of the men is loading his gun, and a dog is trying to get out of the way, while the captain gives the order to advance, and the ensign waves the company's flag.
The dynamic feeling of the painting would originally have been increased by the setting, since Rembrandt had added a balustrade at the left to give more perspective - that, as well as the arch above, was trimmed off the painting in the eighteenth century.
The lighting is intensely dramatic, with a dark, murky background, and just a few of the figures picked out almost as if by spotlights, in Rembrandt's characteristic chiaroscuro treatment.
Rembrandt uses strong colours to focus the viewer's attention; the Captain has a bright crimson sash, the Lieutenant is dressed in creamy yellow, and the little girl - the company's mascot - is in bright white, half-hidden behind a musketeer dressed all in red.
The painting is truly monumental; Rembrandt's original measures three and a half by four metres. But his painting isn't pompous; he has created a baroque theatre of gesture which incorporates gentle comedy as well as flag-waving and action; one old man is nearly falling asleep over his gun, while in the back row another of the characters seems to be laughing at a private joke.
The composition of the picture is masterful. At its centre is the captain's gesturing hand, foreshortened so that it almost looks as if it is bursting out of the picture towards the viewer.
On the left, the flagstaff forms a diagonal pointing directly to the captain and lieutenant, while a single brightly lit pikestaff on the other side provides a second diagonal again leading to the centre of the painting. This pulls together a composition which otherwise might have become chaotic.
The Night Watch are about to march, out of the dark gateway and into the light. That's a stunning way to envision the militia, and through it Rembrandt suggests the emergence of the Dutch nation, and even, perhaps, a broader human message of hope.