In the course of six centuries (1st–6th cen­tury), the Ancient settlement and Fortress of Transmariska, located on the territory of the modern-day town of Tutrakan, played an important role in the defence and functioning of the Roman and early Byzantine limes.
Transmariska came to life at the end of the first half of the 1st century AD. With the arrival of the 1st Thracian-Syrian co­hort in the second century AD, Trans­mariska became an integral part of the Roman Defence of the Lower Danube. In the 2nd and 3rd centuries, Transmariska retained its character - a camp of a not-large military unit and a civilian settle­ment, benefiting from the river’s trans­port capabilities, the ancient road along the limes and the favourable economic conditions of the area. The end of the 3rd century marked the beginning of a new development of the fortification system and the role of Transmariska in the de­fence of the limes. The city became part of a major construction program to sta­bilize the defence power at the Roman border. Emperor Diocletian personally visited Transmariska in 294, as an inscrip­tion has been preserved testifying to this, in which the fortress was called “a pre­sidium”. The castle was one of the four largest military centres of the Lower Dan­ube limes. Here resided the prefect of the second part of the XI Claudius Legion. Under his command were 5 cohorts of the legion. With them he controlled the river bank from the village of Ryahovo to the village of Dolno Ryahovo.
Later in the 5th and 6th centuries Trans­mariska was an episcopal centre. The city was continuously attacked and destroyed by the Goths and Huns. The ancient set­tlement was ruined in the early 17th cen­tury as a result of barbarian invasions.
The Roman and Byzantine fortress, lo­cated under the modern-day city, had an area of 65 decares. From the north­ern part of the fortress revealed are the fortress wall with two square towers with a pavement of stone slabs on the lower level and ceramics on the upper level. The wall had a gate in the middle be­tween the towers and a postern gate in the eastern tower. The southern fortress wall of Transmariska with its two battle towers, one of which with the shape of a horseshoe and the other one fan-shaped, is a significant archaeological monument of culture and an interesting tourist site.
The ancient castle of Transmariska was declared a monument of culture of na­tional importance in 1968.


Under the modern-day town of Tutrakan archaeologists have unearthed remains of a Roman road station and of a fortress that existed in Antiquity, Late Antiquity, Medieval and Ottoman times.