Authorities say a three-alarm fire inside Quincy's old City Hall may have been started by thieves after copper piping.
No one was hurt in the blaze reported at about 1 p.m. Tuesday.
The 170-year-old building is not being used but is undergoing a $9 million renovation project.
The fire started in the rear basement area.
A spokeswoman for the state Fire Marshal says the blaze was likely caused by "an open flame from a cutting torch." There have been no arrests.
Mayor Thomas Koch says the renovation project has been set back six to eight weeks and the construction company's insurance would pay for the damage.
Someone tried to steal copper pipes from the building last weekend.