Fort Istibey (Greek: Οχυρό Ιστίμπεη) is a fortress on Mount Beles, Central Macedonia, at the north border of Greece built to help defend Greece during the World War 2.
It became part of the fortifications of the Metaxas Line, a chain of fortifications along the Greek-Bulgarian borders that were built in the 1930s, named after Ioannis Metaxas, then Prime Minister of Greece.
It is situated 16 km north of Neo Petritsi village at an altitude of 1.339 meters.
The main mission of the fort was to prevent entrance to the country from Bulgaria. It housed 13 officers and 350 soldiers. Its commander in chief was Ksanthos Pikoulakis.
The fort was active until April 1941, when it was forced to surrender to German troops.
In 1991 the Panhellenic Association of Combatants and Friends of the Forts of Macedonia and Thrace funded the construction of a small museum on this site in commemoration of its role in the Battle of the Forts in April 1941, against invading German forces.
Access to the museum is restricted: permission must be obtained from the military unit stationed at Petrich, which is four kilometres off the Serres-Promachonas National road (Kilkis junction). Foreign nationals must have obtained a special permit from the Hellenic Army General Staff.
The museum contains firearms (rifles, revolvers, pistols and machine-guns) belonging to the Greek and German armies, army uniforms of the time, various personal belongings of the defenders, as well as a map detailing the Battle of the Forts. During visits a film is also shown, which tells the story of the battle at Fort Istibey.