The town of Kula has a population of 4 000 inhabitants and lies at a distance of 32 km southwest of Vidin. Kula is a municipal centre with 8 component settlements. The town owes its present-day name to the big Roman tower in its centre. "Kula" in Bulgarian means "tower". The Hungarian traveler Felix Kanitz first localizes Kastra Martis in XIX c. Later the archaeological research confirms his guesses.

After the conquering of these lands in I^st century all the lands between Danube and the Stara Planina Mountains are included in the Province of Mizia and later begins the construction of the Danube complex of fortified settlements, towers and other facilities. The main centre is Ritzaria (near the village of Archer). At the end of III c. and the beginning of IV c. the border is fortified with new fortresses built on significant places. The Kastra Martis fortress has occupied a strategic place near the most western pass of Vrashka Chuka and has defended the road from Bologna to Singidunum (Belgrade). In 377 Emperor Grecian has passed through the fortress with his legions on the way to Thrace. The fortress has been demolished by Goths, Huns, Avars and Slavs.

After a break of several centuries, when life has died out on the site, the fortification has been partially restored during the period of the Vidin Feudal Kingdom. Near the ruins of the fortress there is a museum exhibition of findings from the excavations on the site. Visitors can see pottery, marble columns, a bronze statue of Venera, tools etc.