A fire that gutted the top floor of the Cabildo, a landmark in New Orleans’ French Quarter where the Louisiana Purchase was signed in 1803, was apparently touched off by workers doing repair work, a fire official said. Wednesday’s fire raged for two hours before being brought under control. The blaze destroyed 18th-Century French furniture stored in the upper floor and consumed the cupola atop the three-story, Spanish-style building, officials said. Smoke and water stained and soaked contents of the first and second floors, where paintings, tapestries, doll and fan collections, Mardi Gras memorabilia, pottery and other items were on display, they said. No injuries were reported. An estimate of damages was not immediately available, but officials said the building remained structurally sound and could be repaired.