Jorn Utzon's Opera House has a heroic quality; indeed, Utzon referred to it himself as a kind of 'cathedral', analogous to a Gothic church in the way that light and movement play across its public spaces. Its complex shell-like roof structures echo Gothic arches in section, but the building breaks with all precedent in its three-dimensional form. Finding a practical solution to the construction of these roofs occupied the architect and the engineer Ove Arup for many years, necessitating considerable experimentation with pre-cast concrete technology. Disputes with his client led to Utzon's withdrawal from the project, and the Opera House looked for a time as if it might be a white elephant. At last, after a 16-year gestation, it opened in 1973 having already become an Australian national icon.