It is one of the least green cities in Europe, but Athens hopes to change that by opening up a long-hidden river that flows through the historic heart of the capital.

In ancient times, the Ilissos River was an idyllic, winding watercourse shaded by plane trees where Socrates once taught.

“Let us turn aside here and go along the Ilissus; then we can sit down quietly wherever we please,” Socrates told his followers, according to an account by Plato, his student.

But in the 1930s, during the rapid urban development of Athens, it was covered over and a tram line was built on top it.

Poor maintenance and the rumble of thousands of trams have caused structural damage to the tunnel beneath the track, and in October the tram line was closed down.

Urban planners have suggested that rather than spending millions of euros on reinforcing the tunnel and repairing the track, the tram line should be diverted along a different route and the river opened up.

They are proposing the creation of a park along a one mile stretch of the formerly forgotten river.