The Palace was the last of the major buildings of Panama Pacific Exposition of 1915 to be started; construction began December 8, 1913. The original columns and Rotunda were framed in wood, and covered with "staff", a mixture of plaster and burlap-type fiber. It was the largest building ever to be made of that material. When the ashes of the Exposition were cleared, all that was left was the Palace of Fine Arts. Then, in the late 1950's, a group of dedicated citizens, led by philanthropist Walter S. Johnson, initiated a drive to rescue the Palace from planned demolition and restore it to its former glory. On July 20, 1964, a contract was awarded and the reconstruction began. Workers carefully removed original design elements from which molds were made. The rotunda, colonnade and all except the steel framework of the gallery were torn down and replaced with concrete castings. In September, 1967, work was completed of a stripped-down version of the original. The addition of the remaining original colonnades was completed in January, 1975 - a gift from Walter S. Johnson to the city and the people of San Francisco. The gallery area now houses the Palace of Fine Arts Theatre and the Exploratorium. The theatre, which seats 1,000 in a continental-style configuration, was added in 1970. The Palace of Fine Arts Theatre is operated by the Palace of Fine Arts League, Inc., a non-profit corporation.