Fort Istibey (Greek: Οχυρό Ιστίμπεη) is a fortress on Mount Beles, Central Macedonia, on Greece's northern border with Bulgaria, that was built to help defend Greece during World War II.

Fort Istibey
Part of the Metaxas Line
External view of the fortress
Fort Istibey
Coordinates	41°20′24″N 23°13′52″E / 41.340°N 23.231°E / 41.340; 23.231
Type	Fort
Site information
Owner	Greek Army
Controlled by	Greece

It became part of the fortifications of the Metaxas Line, a chain of fortifications along the Greek-Bulgarian border that was built in the 1930s and named after Ioannis Metaxas, then Prime Minister of Greece.

It is situated 16 km north of the village of Neo Petritsi 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 obtain 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 that tells the story of the battle at Fort Istibey.