Hymettus, also Hymettos (Υμηττός, phonetic spelling Imitós) is a mountain range in the Athens area, East Central Greece. It is also colloquially known as Trellos or Trellovouno (crazy mountain), probably coming from French colonials in the 15th or 16th century , calling the mountain Tres Long. The height is 1,026 m at Evzonas and the length is 16 km (10 mi) between Athens and the Saronic Gulf and 6 to 7 km from east to west. In the ancient times, the highest point was known as Mega Ymittos and the southern Elattona (Ελάττονα) and Anydro Ymitto (Άνυδρο Υμηττό) (today Mavrovouni (Μαυροβούνι meaning black mountain) and Kontra (Κόντρα)). It was noted for its thyme honey. Marble has been quarried since antiquity. The neighboring communities that surround the mountain are Athens, Zografou, Kaisariani, Vyronas, Ilissia (a region of Zografou), Ymittos, Helioupolis, Argyroupoli, Elliniko, Glyfada, Voula and Vouliagmeni in the west, Varkiza, Vári, Markopoulo and Paeania to its east, and Papagou, Holargos, Aghia Paraskevi, Gerakas and Glyka Nera. Most of the forest is in the north, and much of the mountain is rocky, deforested, grassy and made out of limestone.
Major campuses of the Athens University and the National Technical University (collectively called "University Town") are located on the west-facing slope, between the newly-built "Hymettus Ring", a ring road connected with the Attiki Odos freeway with five interchanges beginning with Y and filled with tunnels, and the Athens urban sprawl. A transmitter park for all major TV and radio stations is located at the top of the mountain. Built up urban areas almost surround the entire mountain range. Access to the top of the mountain is restricted to authorized vehicles for maintenance of the towers.
Almost all of Athens, its eastern suburbs and the new airport can be seen from the mountain top along with the mountains of Parnitha to its northwest, Penteli to its north and Aegaleo to its west. The valley areas that create the lowest passes are to the south and one further south.
The mountain ranges features about six to seven landfills in the western part and another in the eastern part.
Its landfills were added in the 1950s and Katechaki Avenue later on. The western part of the mountain range were planted with trees in the 1950s. Housing developments were built after World War II and the Greek Civil War which founded the city of Papagou by its slopes and expanded to the south as late as the 1980s by its edges. Marble was mined in the western half between the 1960s and the 1990s and more smaller mines were mined. Mining is now rare since most of its resources are not allowed to be mined.
Hymettus was struck by a forest fire around 3 PM (15:00) local time on July 16, 2007. Municipal fire trucks, choppers, nearby residents and six planes were racing to stop the fire from the nearby Saronic Gulf area. It took around two hours to stop the blaze. The blaze was at critical level after it started and flames were burning as far as Ilioupoli but it didn't reach south. Firefighters were fighing the blaze at a hilltop near the avenue and several fire trucks were parked on the avenue with most of the fire occurring at the most forested part of the mountain. Near the late-afternoon, the fire declined and by sunset the fire was out, burning forest in the vicinity of the urban area and south of Katechaki Avenue.
Its affected level was in east Kaisariani and Vyronas along with Kareas where the smoke blanketed over its residential area, shutting down Katechaki Avenue for several hours in its entire length south of the Ymittos Ring and parts of Kareas Avenue blocking the bypass traffic of Athens.
The suspected cause of the fire is arson.