Behind its discreet facade on Beacon Hill, steps from the State House, the Boston Athenaeum revisits one of the great photographic portraits of this city. In the mid-1970s, Magnum photographer Constantine Manos spent months roaming Boston with a 35mm Leica for the city’s bicentennial, shooting thousands of frames of protests, parades, flea markets, diners, and everyday neighbors from the Common to Franklin Park. Fifty years on, the Calderwood Gallery brings that archive back into focus.

What makes the show more than nostalgia is the detective work around it: the Athenaeum has been asking Bostonians to help identify the people in the pictures and add their own memories and oral histories. It suits anyone who loves street photography or old Boston — and seeing it doubles as an excuse to step inside one of the country’s oldest independent libraries.