Christiaanse worked with Rem Koolhaas' architecture firm, OMA, where he was made a partner in 1983 at the age of 30, and worked for the firm until 1989. After OMA, he founded Kees Christiaanse Architects and Planners (KCAP, in Rotterdam, 1989) and ASTOC Architects and Planners (in Cologne, 1990); he worked with ASTOC until 2002. He was also artistic director of the Dutch Building Department from 1993 to 1996. From 1996 to 2003 he was a professor of architecture and urban planning at the Technical University of Berlin, and is now the Chair of Architecture and Urbanism in the Institute for Urban Design at ETH in Zürich. Two monographs on Christiaanse's work have been published, and an exhibition of the work done by his firms, "The City as Loft," was held at De Singel in Antwerp in 2003. He is known for his urban planning work and "has quietly become the power behind the throne of Dutch architecture." He now lives and works in Zurich. Christiaanse was the curator of the 4th International Architecture Biennale Rotterdam, and takes on large-scale projects such as the development of neglected areas for the 2012 Summer Olympics. His latest project is the design of a masterplan for an "engineering campus" (or "science park") in the Bavarian city of Augsburg, a 70-acre (280,000 m2) project for which the state government (Freistaat Bayern) and the city are contributing 60 million Euros. Urban planning philosophy Of particular interest to Christiaanse is the modern city, especially its openness or lack thereof. His designs as well as his public statements propagate the idea of "mixed communities," as he explained in an interview, to counteract the modern move toward gated communities and to increase different kinds of interactions among citizens. Such interactions, and the social control that comes along with it, also increase security, a concern in many European lower-income neighborhoods. The buildings to be built in such new neighborhoods Christiaanse calls "socializing machines." The metaphor Christiaanse often uses, of the city as a tree, is borrowed from architect and urban theorist Christopher Alexander, whose 1965 essay "A City Is Not A Tree" had suggested that cities grow like trees at their peril, with branches only connected to each other via the trunk. Alexander's fear, Christiaanse suggests, has become real, according to a keynote speech he delivered at the Holcim Forum 2007 for the Holcim Foundation, which is the key to his lament that "The city becomes a tree [the urban landscape becomes a forest of trees]." In a presentation given to the Urban Age South America Conference, December 2008, he gave some characteristics of the openness he wants cities to encourage in order to prevent this segmentation. Cities should be (or have): Walkable Fine maze public space grid Active street front typologies Mix use mix size mi[x] social mix age No style.