Ideal geometric forms such as circles and squares have an enduring appeal for architects, but are rarely suited to the contingent demands of modern building programmes and urban sites. Tietgen Dormitory, completed in Copenhagen in 2006, is a triumphant exception. Named after the leading Danish financier C.F. Tietgen (1829-91) and winner of numerous national and international architectural awards, the project began life as the dream of Nordea-fonden who wished to offer students a collegiate alternative to the contemporary norm of living individually or in small groups in private accommodation. Following an architectural competition the foundation's vision was given form by the leading Danish architects Lundgaard and Tranberg, who found that the circular geometry, so rare in modern architecture, provided both a telling contrast to the orthogonal discipline of the surrounding buildings in the new-town district of Ørestad North and a perfect way of balancing community and privacy. Tietgen Dormitory is a unique celebration of a unique project. Through numerous specially prepared drawings and photographs and two short but evocative essays, it invites the reader to take an imaginative journey around the building and through the long and fascinating history of circular structures in world architecture - from vernacular dwellings to prefabricated houses, theatres to sports stadia, churches to ideal town plans.