Marvelous metaphor by Shakespeare, suggesting (to me) that the foment and energy of a city like London forges thought among its people. Something taut and elemental here, with the din and heat of a blacksmiths workshop echoing the noise and bustle of a great city.  

But now behold,

In the quick forge and working-house of thought,

How London doth pour out her citizens!

Source: William Shakespeare, Henry V, V, Prologue, 22-24

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