Civilizations, as well as forests, may be swept by devastating fires. But sometimes in the aftermath, the very ashes nourish the soil, and gradually a vigorous new growth rises. It is an inspiring but terrible kind of reforestation-historical progress by way of apocalypse.

Phoenix industries arise from rubble. Cities recrystallize. The forest obliviously forgives the fire. In 50 years the new order may become so lush that hardly anyone remembers the shock and despair, the flames and the blackened earth and the evil. The nitrates work a miracle of cultivation. A population that had descended from Bach to barbarism may find its way, sadder but wiser, toward Bach again.

That, anyway, is the hope. And so a society, recovering, may build a memento mori-a tribute to the civilizing influence of memory. In Bonn the tribute takes the form of a three-story museum called the Haus der Geschichte (House of History)-an archaeological inventory through which a younger generation may trace the astonishing process of European death and rebirth over the past 50 years.