The vanished history of black people in Boston is visible again to anybody with a smartphone, thanks to Arizona State University journalism professor Retha Hill. Her free “augmented reality” Black History app offers a video tour of the city’s African American history.

Hill's program displays historical information on the phone when the user is close to a significant site. Just launch the software, and take a stroll through Boston with one eye on the phone’s screen. If you’re near any of the two dozen or so landmarks featured in the program, you’ll get an education.

Here are some of the landmarks it lists.