Most of the landmarks of contemporary architecture are the works of a small group of architects who work on an international scale. Many were designed by architects already famous in the late 20th century, including Mario Botta, Frank Gehry, Jean Nouvel, Norman Foster, Ieoh Ming Pei and Renzo Piano, while others are the work of a new generation born during or after World War II, including Zaha Hadid, Santiago Calatrava, Daniel Libeskind, Jacques Herzog, Pierre de Meuron, Rem Koolhaas, and Shigeru Ban. Other projects are the work of collectives of several architects, such as UNStudio and SANAA, or giant multinational agencies such as Skidmore, Owings & Merrill, with thirty associate architects and large teams of engineers and designers, and Gensler, with 5,000 employees in 16 countries.