Walbrook's the name of a ward, a street and a subterranean river in the City of London. Underground river The river played a key role in the Roman settlement of Londinium, the city now known as London. It's thought that the river acquired its name from the fact that it ran through or under the London Wall. The stream started in what's now Finsbury and flowed right through the centre of the walled city into the River Thames, near to where Cannon Street Railway Bridge's now located, splitting the… (More on Walbrook)