Line 4 began as something else entirely. In the metro plans of the late 1990s, the new route was imagined not as its own line but as two branches grafted onto the existing Lines 2 and 3 - one reaching up toward Galatsi and Alsos Veikou, the other curving through the eastern suburbs. By 2005 that idea had been scrapped. The public works minister Georgios Souflias announced that the branches would instead be welded into a single independent line, U-shaped on the map, because bolting them onto the older lines would have created what he called significant structural and operational weaknesses. Athens had learned that a fast-growing metro needs its own spine, not borrowed ones. Over the following years the plan was refined, stations renamed and relocated, until the first phase - Alsos Veikou to Goudi, 12.8 kilometers and 15 stations - took its present shape.

Not every neighborhood welcomed the dig. When construction crews moved toward Exarcheia Square in 2022, residents pushed back hard. Exarcheia has a fierce identity as a historically leftwing and anarchist quarter, and many locals saw the planned station as the leading edge of gentrification - a project that would, they feared, sand away the character of one of Athens' most defiant public spaces. Protests broke out, and sixteen people were detained. The work paused, then resumed once the demonstrations ended, and the station rose at Exarcheia Square after all. It was a reminder that a subway is never only an engineering problem. A station entrance changes who walks a street, who can afford to live near it, and what a neighborhood becomes - and the people who live there know it.

Engineering a metro beneath an ancient, crowded city means going down, sometimes far down. Every confirmed station on Line 4 is underground, built with two tracks and two side platforms. The deepest, at Elikonos in Galatsi, will sit 36.4 meters below the surface - named for the Elikonas hill that rises beside it - with Ilisia station the runner-up at 34.7 meters. The tunnel-boring machines Athina and Niki have ground steadily through more than twelve kilometers of rock, with officials targeting the completion of the bored tunnel. The work has not been without alarm: members of the opposition parties Syriza and the Communist KKE raised concerns in parliament, pointing to a letter from the contractor warning that the tunnel construction had departed from certain studies in ways that could pose safety and financial risks. Building under a living city is slow, contested, and unforgiving of shortcuts.

Line 4 is the first stage of something much larger. If every planned section is built, the line could eventually stretch about 38 kilometers with 35 stations, reaching north toward Marousi and Lykovrysi and feeding into a proposed Line 5. The European Investment Bank is covering 800 million euros of the first phase's cost, with the rest from Greek and EU funds. Construction began in 2021 and is officially scheduled to finish in 2029, though realistic estimates push that toward 2030 - the familiar arithmetic of a megaproject tunneling through a 3,000-year-old city. For now the line lives mostly in the dark, in the steady grind of Athina and Niki, a route Athenians can already trace on planners' maps but cannot yet ride. When it opens, it will close gaps the older lines never reached.