The building was designed by John Parkinson, John C. Austin, and Albert C. Martin, Sr., and was completed in 1928. Dedication ceremonies were held on April 26, 1928. It has 32 floors and, at 454 feet (138 m) high, is the tallest base-isolated structure in the world, having undergone a seismic retrofit from 1998 to 2001 so that the building will sustain minimal damage and remain functional after a magnitude 8.2 earthquake.[7] The concrete in its tower was made with sand from each of California's 58 counties and water from its 21 historical missions.[2] City Hall's distinctive tower was based on the shape of the Mausoleum of Mausolus,[8] and shows the influence of the Los Angeles Public Library, completed soon before the structure was started.