At 5 p.m. Monday one of the longest pieces of performance art on record, and certainly the one with the largest audience, comes to an end. Since her retrospective opened at the Museum of Modern Art on March 14, the artist Marina Abramovic has been sitting, six days a week, seven hours a day in a plain chair, under bright klieg lights, in MoMA’s towering atrium. When she leaves that chair Monday for the last time, she will have clocked 700 hours of sitting.

During that time her routine seldom varied. Every day she took her place just before the museum doors opened and left it after they closed. Her wardrobe was consistent: a sort of concert gown with a long train, in one of three colors (red, blue and white).

Always her hair, in a braided plait, was pulled forward over her left shoulder. Always her skin was an odd pasty white, as if the blood had drained away. Her pose rarely changed: her body slightly bent forward, she stared silently and intently straight ahead.

Image Marina Abramovic sits opposite a visitor at MoMA. Credit... Ruth Fremson/The New York Times

There was one variable, a big one: her audience.

Visitors to the museum were invited, first come first served, to sit in a chair facing her and silently return her gaze. The chair has rarely, if ever, been empty. Close to 1,400 people have occupied it, some for only a minute or two, a few for an entire day.