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craft than the pre-fire eighty-six. In this, the urban plan was a little like his drawing of the fly’s eye; it imposed more clarity than existed in reality. Finally, Wren’s drunk dogs helped him to think about repairing London. The scalpel had permitted anatomists to study the circulation of the blood; that knowledge, applied to circulation of movement in streets, suggested that streets worked like arteries and veins; this was thus the era in which planners began to incorporate one-way streets in their designs. Wren’s circulatory city was commercial in intent, aiming to deal efficiently in particular to create streets that moved goods to and from the necklace of warehouses draped along the Thames. But this design lacked the equivalent of a human heart, one central, coordinating square. Roger Pratt, an old enemy, argued that Wren’s plan should be defeated just because it was exploratory surgery, raising more problems than it answered. The city fathers could not move forward, Pratt said, ‘‘being that no man can tell how to offer any acceptable design till they [the results] be determined’’ in advance. To this bureaucratic objection, Wren’s riposte lay in the virtue of experimentation; his was, in the words of a contemporary, a ‘‘fertile power of imagination’’ whose very fertility incorporated incompleteness and ambiguity.∞π I’ve dwelt on this monumental event in part because disasters of a kindred sort appear today when cities like New Orleans or Gloucester are flooded; global warming may well bring further, sudden destruction. The issues Wren’s age faced are still ours: whether to restore what existed in form before or to make a more dynamic, innovative repair. The second option may seem too technically demanding; no adequate, fit-for-purpose tools lie to hand. Wren’s story might strengthen the desire to pursue the second option; it reveals how limited and uncertain tools can play a play a positive role in change, by stimulating imagination and so expanding competence. We are all familiar with the saying of Heraclitus that ‘‘no man ever steps in the same river twice, because it is not the same river and not the same man.’’ The craftsman