Tulsa includes many structures built during the Oil Boom in the 1920s and 1930s, including Art Deco buildings such as Boston Avenue Methodist Church and Tulsa Union Depot. Waite Phillips left a significant architectural impact on downtown Tulsa through the Philtower and Philcade Building. Other notable downtown Tulsa buildings include the Exchange Bank Building (today known as the 320 South Boston Building, the Cosden Building (later expanded into today's Mid-Continent Tower), Atlas Life Building, Holy Family Cathedral, Holy Trinity Greek Orthodox Church, and the Mayo Hotel. Known for a time as "Terra Cotta City", Tulsa hosted the International Sixth Congress on Art Deco in 2001. The core downtown area was designated on the National Register of Historic Places as the Oil Capital Historic District in 2010.