"THOUGH the offices of Dombey and Son were within the liberties of the City of London, and within hearing of Bow Bells, when their clashing voices were not drowned by the uproar in the streets, yet were there hints of adventurous and romantic story to be observed in some of the adjacent objects. Gog and Magog held their state within ten minutes' walk; the Royal Exchange was close at hand; the Bank of England, with its vaults of gold and silver `down among the dead men' underground, was their magnificent neighbour."

Gog and Magog are the traditional guardians of London. Here is a long but interesting URL about them:
http://www.lordmayorsshow.org/hist/gogmagog.shtml