There is no sadder tale in the annals of architecture than the virtual disappearance of the defining architectural form of the Modern Movement - publicly sponsored housing.

The financial benefits of prefabrication have never been as large as its advocates predicted, for although some labor costs can be reduced by machine manufacturing, on-site assembly of any building still depends to some extent on the handwork of skilled craftsmen.

Avant-garde architects have never been able to depend on the support of the establishment, since the customary patrons of this most conservative and slowly moving art form have historically been resistant to innovation and experiment.

Architecture traditionally has been the slowest of art forms. It was not unusual for great cathedrals to take centuries to complete, with stylistic changes from Romanesque to Gothic or Renaissance to Baroque as common as the addition of chapels or spires. But because the function remained the same, the form could be flexible and its growth organic.

Renzo Piano and Richard Rogers's Centre Georges Pompidou of 1971-1977 - the true prototype of the modern museum as popular architectural spectacle - wound up costing so much more than planned that the French government solved the shortfall by cutting support for several regional museums.

The truth be told, the World Trade Center was neither a very good work of architecture nor a very successful piece of urbanism. Its shortcomings were somewhat mitigated by the westward and southward expansion of the World Financial Center and Battery Park City during the 1980s.

Architecture is not a profession for the faint-hearted, the weak-willed, or the short-lived.