The regional location of the Bessi, in the mountains and North-West of the Dii tribe.
The Bessi was once an independent Thracian tribe that dwelled in territories ranging from Moesia over to Mount Rhodope in southern Thrace, where they are often mentioned dwelling somewhere around Haemus which was a mountain range that separated Moesia from Thrace and from Mount Rhododpe to the northern parts of Hebrus. Herodotus was known to describe them as priestly-caste among the Satrae, where the Bessi were being interpreters of a prophetic utterance which was given to them by a priestess in an oracular shrine of Dionysus which is seen located top of a mountain.
In 72 BC, the proconsul of Macedonia; Marcus Terentius Varro Lucullus defeated the Bessi and later Strabo provided a record in where the Bessi were described as one of the most fierce independent Thracian tribes that dwelled all around the Haemus range and possessed the greater areas of that mountain chain. He calls them brigands among brigands and that they had an addiction for plundering.
Mommsen says the capital of the Bessi was supposedly Uscudama which is now known as Edirne in modern Turkey but the real place seems to be Bessapara, which is now Sinitovo located next to Pazardzhik, Bulgaria.
The Diobesi are also thought to be a union of sorts between the Besai and the Dii where Pliny the Elder revealed several divisions of the Bessi.
Appian writes that they were in fear of Augustus and surrendered to him.
Towards the end of the 4th century, Nicetas who was a Bishop of Dacia brought the gospel to "those mountain wolves" which was what the Bessi were called. His mission was reported successful, where the worship of Dionysus and other Thracian gods eventually were replaced by Christianity.
A Thracian personal name Bessus (attested in Northern Montenegro along with other Thracian names such as Teres) is considered to have the same etymon as Bessi (Wilkes, 1982).
In the 11th century Strategikon text, Cecaumenos the Byzantine historian described the Vlachs from Thessaly (i.,e. the Aromanians of Great Wallachia) as being descendants of ancient Dacians and Bessi who invaded from the area on the Danube, supposedly seeking revenge for the defeat inflicted to their ancestors by Trajan during the Dacian Wars.