With roots at least 7,000 years old, London is an accretion of artifacts old and new, from the remnants of wooden Neolithic settlements buried in the mud of the Thames to gleaming 21st century spires of glass and steel.
The city is so old that the origins of its very name are unknown: it's first recorded title, Londinium, was provided by the Romans in the first years of the Common Era, but the etymology of the word is completely obscure.
This extends to some of its architecture: the London Stone, an irregular block of limestone at 111 Cannon Street, has been guarded by an iron grill for centuries, but no-one has known what the stone's purpose is, or why it is there, for the past 1000 years.