The Walbrook stream played a key role in the Roman settlement of Londinium, the town now known as London. It is thought to get its name from the fact that it ran through or under the London Wall. The stream started in what is now Finsbury and flowed, right through the centre of the walled town into the river Thames, near to where Cannon_Street_Railway_Bridge is now located, splitting the town in two. It was probably used for fresh drinking water and also carrying sewage down to the Thames. The Romans built a temple to Mithras on the east bank. The temple was discovered and subsequently excavated during rebuilding work after World War 2. The Roman Governor's palace was also located on the east bank of the stream, near to its entry point into the Thames.
The stream now runs completely underground, the only evidence above ground that the stream is there is a street called Walbrook, that runs parallel to its course. On the street is a church called St Stephen, which originally stood on the west bank of the stream, but was rebuilt around 1439 on the east side. In 1666 the church burnt down in the Great Fire of London and Sir Christopher Wren built a new church there in 1672 to replace it, which still stands there today.