The 60,000-pound crane was sitting on gravel and pebbles in the outdoor area of the Rathskeller restaurant in the 115-year-old Athenaeum when it tipped onto its side, The Indianapolis Star reported Monday.
Capt. Rita Burris of the Indianapolis Fire Department said the veteran crane operator, Roger Browning, reported feeling the ground shift before the 90-foot boom tilted and crashed into the roof of the building's YMCA gymnasium.
The sprinkler system turned on and about 185 people ran outside, the newspaper said.
"It absolutely could have been a lot worse," Burris said. "It's unfortunate that this historic building suffered this damage, but it can be repaired."
Two people suffered minor injuries and were taken to Methodist Hospital. There was no immediate information on the condition of the third person, the Star said.
The building, designed by Bernard Vonnegut and Arthur Bohn, opened in 1894 as Das Deutsche Haus (The German House) as a cultural, social and recreational center for German organizations.
The name was changed to the Athenaeum in 1918 because of post-World War I anti-German sentiment.