What is the smallest city in the world with a heavy rail metro?

Question

By population

Answer 1

The City of London is one square mile in area.

It is served, inter alia, by Bank Station on the Central Line of the London Underground.

Answer 2

In Europe, most metro lines reach out into the suburbs. So you might find it on the south ring of Metro Madrid.

If you are talking about suburb trains, you might find it on the lines out of Karlsruhe/Germany or Offenburg/Germany. Those reach out into the Black Forrest with small towns and villages along the lines, some even with two stops.

Answer 3

Vatican City - served by the Rome Metro?

Answer 4

D.C