In the beginning of the ХІ century the Klyuch gorge was mentioned in the written sources in relation to the attempts of the Byzantine emperor Basil II to regain the territories on the Balkans. “The emperor couldn’t stop himself from the invasion of the Bulgarian lands and the mass destruction of everything on his way”. ”That’s why he (Samuil) decided to dig ditches and build protection palisades against the emperor’s invasion in Bulgaria. And because he was aware of the exact invasion route of the emperor - through  Kimva Long and Klaidion (Klyuch), he decided to block it.”

The ground fortification, built on a low slope, known as the fortress of Saumil is a central unit in the defence system. It blocks the way to the Klyuch gorge - the only accessible place for actions of big armies in this region.

The defence system blocks the way to the gorge from the high slopes of Belasitsa, south of the Klyuch village to the Ograjden Mountain. The excavations, led by the scientist Dimka Stefanova of the museum in Blagoevgrad, started in 1968 and finished in 1976 with a few interruptions. It was found that the hill, surrounded by the ancient Pontos river ( Strumeshnitsa) has been inhabited since the Iron age. The Thracian village existed up until I century B.C. After that, the life on the hill simply vanished. Much later in 7th c. a Slav village was built.

The significant number of coins from the Joan Tsimiski’s period, found in the ashes on the floor of the dwelling places, make us belief that, the arson of the village is related to one of the marches of Basil II.
The constructed, ground fortification on the hill consists of 3 ramparts and 2 ditches in order to block the Klyuch gorge. The only tower situated on the top and most protected part of the hill with a rocky base and a wooden upper part had no protective functions. It was used as a watch-tower.